mirror of https://github.com/dynup/kpatch
kpatch-build: clarify ppc64le comments
Clarify some of the comment wording in the new ppc64le code.
This commit is contained in:
Josh Poimboeuf
parent
e3ccff0cab
commit
339938c0a9
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@ -3,9 +3,9 @@ KPATCH_BUILD ?= /lib/modules/$(shell uname -r)/build
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KPATCH_MAKE = $(MAKE) -C $(KPATCH_BUILD) M=$(PWD)
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LDFLAGS += $(KPATCH_LDFLAGS)
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# ppc64le kernel modules are expected to compiled with
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# -mcmodel=large flag. This enable 64-bit relocations,
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# instead of 32-bit offset from TOC pointer.
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# ppc64le kernel modules are expected to compile with the
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# -mcmodel=large flag. This enables 64-bit relocations
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# instead of a 32-bit offset from the TOC pointer.
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PROCESSOR = $(shell uname -p)
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ifeq ($(PROCESSOR), ppc64le)
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KBUILD_CFLAGS_MODULE += -mcmodel=large
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@ -184,10 +184,11 @@ static int rela_equal(struct rela *rela1, struct rela *rela2)
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* 00000000000000b4 000000b90000000a R_PPC64_REL24 0000000000000000 printk + 0
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* 00000000000000bc 000000a10000000a R_PPC64_REL24 0000000000000000 dump_stack + 0
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*
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* with -mcmodel=large on ppc64le, gcc might generate entries in .toc section for symbol
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* reference in relocation sections. There are chances of symbol referenced by toc + offset
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* may point to different symbols in original and patched .o. Compare the symbols by
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* reading its corresponding toc + offset rela from .toc section.
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* With -mcmodel=large on ppc64le, GCC might generate entries in the .toc
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* section for relocation symbol references. The .toc offsets may change
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* between the original and patched .o, so comparing ".toc + offset" isn't
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* right. Compare the .toc-based symbols by reading the corresponding relas
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* from the .toc section.
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*/
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if (!strcmp(rela1->sym->name, ".toc") &&
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!strcmp(rela2->sym->name, ".toc")) {
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@ -237,9 +238,8 @@ static void kpatch_compare_correlated_rela_section(struct section *sec)
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struct rela *rela1, *rela2 = NULL;
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/*
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* Don't compare relocation entries for .toc section.
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* .toc and .rela.toc sections are included as standard
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* elements.
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* On ppc64le, don't compare the .rela.toc section. The .toc and
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* .rela.toc sections are included as standard elements.
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*/
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if (!strcmp(sec->name, ".rela.toc")) {
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sec->status = SAME;
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@ -1011,10 +1011,12 @@ static void kpatch_replace_sections_syms(struct kpatch_elf *kelf)
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#ifdef __powerpc__
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/*
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* With -mcmodel=large, the relative relocation or
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* R_PPC64_REL24 type is limited to functions only.
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* rela->sym->sec should have been replaced with it's
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* section symbol already. If not bail out.
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* With -mcmodel=large, R_PPC64_REL24 is only used for
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* functions. Assuming the function is bundled in a
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* section, the section symbol should have been
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* replaced with a text symbol already. Otherwise,
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* bail out. If we hit this situation, more core is
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* needed here to calculate the value of 'add_off'.
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*/
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if (rela->type == R_PPC64_REL24)
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ERROR("Unexpected relocation type R_PPC64_REL24 for %s\n", rela->sym->name);
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@ -1220,9 +1222,9 @@ static void kpatch_include_standard_elements(struct kpatch_elf *kelf)
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}
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/*
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* rela.toc section holds reference to symbols,
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* referred by function section relocation
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* entries. Include all of the symbols.
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* On ppc64le, the .rela.toc section refers to symbols which
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* are needed for function symbol relocations. Include all the
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* symbols.
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*/
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if (!strcmp(sec->name, ".rela.toc"))
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{
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@ -2254,8 +2256,8 @@ static void kpatch_create_intermediate_sections(struct kpatch_elf *kelf,
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sym_objname = objname;
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/*
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* function prologue generated by gcc6 on ppc64le has
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* the sequence:
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* On ppc64le, the function prologue generated by GCC 6
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* has the sequence:
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*
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* .globl my_func
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* .type my_func, @function
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@ -2264,12 +2266,10 @@ static void kpatch_create_intermediate_sections(struct kpatch_elf *kelf,
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* .reloc ., R_PPC64_ENTRY ; optional
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* ld r2,-8(r12)
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* add r2,r2,r12
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* .localentry my_func, .-my_func
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* .localentry my_func, .-my_func
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*
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* first entry past function global entry point is optional
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* and has the relocation type R_PPC64_ENTRY. We should *not*
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* skip this entry while building up the rela list, rather
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* skip it's lookup.
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* The R_PPC64_ENTRY is optional and its symbol might
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* have an empty name. Leave it as a normal rela.
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*/
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if (rela->type == R_PPC64_ENTRY)
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continue;
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@ -2291,17 +2291,19 @@ static void kpatch_create_intermediate_sections(struct kpatch_elf *kelf,
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*/
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#ifdef __powerpc__
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/*
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* An exported symbol, might be local to an object file
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* and any access to the function might be through localentry
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* (toc+offset) instead of global offset.
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* An exported symbol might be local to an
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* object file and any access to the function
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* might be through localentry (toc+offset)
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* instead of global offset.
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*
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* fs/proc/proc_sysctl::sysctl_head_grab:
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* 166: 0000000000000000 256 FUNC GLOBAL DEFAULT [<localentry>: 8] 42 unregister_sysctl_table
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* 167: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND .TOC.
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*
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* These type of function have the sym->type == STT_FUNC, treat them as local
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* symbol. This creates an entry under klp.relocations and relocation
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* is handled by livepatch.
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* These type of symbols have a type of
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* STT_FUNC. Treat them like local symbols.
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* They will be handled by the livepatch
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* relocation code.
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*/
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if (lookup_is_exported_symbol(table, rela->sym->name)) {
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if (rela->sym->type != STT_FUNC)
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@ -201,8 +201,10 @@ static void create_klp_relasecs_and_syms(struct kpatch_elf *kelf, struct section
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* 0000000000000058 0000003900000026 R_PPC64_ADDR64 0000000000000000 __per_cpu_offset + 0
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* [...]
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*
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* when more .o files are linked together, the .toc entries might get re-arranged. Capture new .toc rela
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* offset value, which will be used below to setting the rela->addend. */
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* On ppc64le, when .o files are linked together, the .toc
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* entries might get re-arranged. Capture the new .toc rela
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* offset value, which is used below to set the rela->addend.
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*/
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toc_offset = rela->addend;
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base = rela->sym->sec;
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@ -245,10 +247,11 @@ static void create_klp_relasecs_and_syms(struct kpatch_elf *kelf, struct section
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rela->offset = krelas[index].offset;
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/*
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* gcc6 adds offset for 0x8 for every local function entry in
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* .toc section, for avoiding setup of toc but when the previously
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* local function becomes global, toc is anyways setup. So remove
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* the wrong addend.
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* GCC 6+ adds 0x8 to the offset of every local function entry
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* in the .toc section, for avoiding the setup of the toc when
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* the function is called locally. But when the previously
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* local function becomes global, we don't want to skip the
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* .toc setup anymore.
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*/
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if (!strcmp(base->name, ".toc") &&
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rela->sym->type == STT_FUNC && rela->sym->bind == STB_LOCAL) {
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@ -160,12 +160,12 @@ gcc_version_check() {
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return 1
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fi
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# On ppc64le, livepatch relies on gcc support for -mprofile-kernel flag.
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# Script with differnet checks is run during kernel build, to ensure that
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# the required gcc supports is available. This check is done during kernel
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# build by:
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# <linux-sources>/arch/powerpc/tools/gcc-check-mprofile-kernel.sh
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# Postpond the check until kernel build, instead of duplicating it here.
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# On ppc64le, livepatch needs the GCC -mprofile-kernel flag. A script
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# is run during the kernel build to ensure the flag is present:
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#
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# <linux>/arch/powerpc/tools/gcc-check-mprofile-kernel.sh
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#
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# Postpone the check to the kernel build instead of duplicating it here.
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if [[ $ARCH = "ppc64le" ]]; then
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return
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else
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@ -85,8 +85,7 @@ int is_debug_section(struct section *sec)
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(((1 << (((other) & STO_PPC64_LOCAL_MASK) >> STO_PPC64_LOCAL_BIT)) >> 2) << 2)
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/*
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* function prologue generated by gcc6 on ppc64le has
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* the sequence:
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* On ppc64le, the function prologue generated by GCC 6+ has the sequence:
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*
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* .globl my_func
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* .type my_func, @function
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@ -95,15 +94,12 @@ int is_debug_section(struct section *sec)
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* .reloc ., R_PPC64_ENTRY ; optional
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* ld r2,-8(r12)
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* add r2,r2,r12
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* .localentry my_func, .-my_func
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* .localentry my_func, .-my_func
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*
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* my_func is resolved by .TOC.-my_func to a 64-bit offset stored
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* above the global entry point. my_func st_value is set 0x8, for
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* calling into the .localentry of the function.
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*
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* Number of instructions between global and local entry point of a
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* function is mostly 8 instructions. i.e st_other == 3. The count of
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* instruction can be decoded only for local function symbols.
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* my_func is the global entry point, which, when called, sets up the TOC.
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* .localentry is the local entry point, for calls to the function from within
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* the object file. The local entry point is 8 bytes after the global entry
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* point.
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*/
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static int is_localentry_sym(struct symbol *sym)
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{
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@ -381,6 +377,7 @@ void kpatch_create_symbol_list(struct kpatch_elf *kelf)
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}
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sym->sec->sym = sym;
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} else if (sym->type == STT_SECTION) {
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sym->sec->secsym = sym;
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/* use the section name as the symbol name */
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@ -15,9 +15,11 @@ if [[ "$TOOLCHAINCMD" = "gcc" ]] ; then
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while [ "$#" -gt 0 ]; do
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if [ "$1" = "-o" ]; then
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obj=$2
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# skip copying the original .o files, when .tmp_mc_*.o
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# is passed from recordmcount.pl.
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# skip copying the temporary .o files created by
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# recordmcount.pl
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[[ $obj = */.tmp_mc_*.o ]] && break;
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[[ $obj = */.tmp_*.o ]] && obj=${obj/.tmp_/}
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case "$obj" in
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*.mod.o|\
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