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create-diff-object: handle reference to end of section
Deal with a special case where gcc needs a pointer to the address at the end of a data section. This is usually used with a compare instruction to determine when to end a loop. The code doesn't actually dereference the pointer so this is "normal" and we just replace the section reference with a reference to the last symbol in the section. Note that this only catches the issue when it happens at the end of a section. It can also happen in the middle of a section. In that case, the wrong symbol will be associated with the reference. But that's ok because: 1) This situation only occurs when gcc is trying to get the address of the symbol, not the contents of its data; and 2) Because kpatch doesn't allow data sections to change, &(var1+sizeof(var1)) will always be the same as &var2. Fixes: #553
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@ -1369,7 +1369,44 @@ void kpatch_replace_sections_syms(struct kpatch_elf *kelf)
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start = sym->sym.st_value;
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end = sym->sym.st_value + sym->sym.st_size;
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if (rela->addend + add_off < start ||
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if (!is_text_section(sym->sec) &&
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rela->type == R_X86_64_32S &&
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rela->addend == sym->sec->sh.sh_size &&
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end == sym->sec->sh.sh_size) {
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/*
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* A special case where gcc needs a
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* pointer to the address at the end of
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* a data section.
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*
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* This is usually used with a compare
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* instruction to determine when to end
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* a loop. The code doesn't actually
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* dereference the pointer so this is
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* "normal" and we just replace the
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* section reference with a reference
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* to the last symbol in the section.
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*
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* Note that this only catches the
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* issue when it happens at the end of
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* a section. It can also happen in
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* the middle of a section. In that
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* case, the wrong symbol will be
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* associated with the reference. But
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* that's ok because:
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*
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* 1) This situation only occurs when
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* gcc is trying to get the address
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* of the symbol, not the contents
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* of its data; and
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*
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* 2) Because kpatch doesn't allow data
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* sections to change,
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* &(var1+sizeof(var1)) will always
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* be the same as &var2.
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*/
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} else if (rela->addend + add_off < start ||
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rela->addend + add_off >= end)
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continue;
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