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musl/tools
Alex Dowad 35b3312b6f Build process uses script to add CFI directives to x86 asm
Some functions implemented in asm need to use EBP for purposes other
than acting as a frame pointer. (Notably, it is used for the 6th
argument to syscalls with 6 arguments.) Without frame pointers, GDB
can only show backtraces if it gets CFI information from a
.debug_frame or .eh_frame ELF section.

Rather than littering our asm with ugly .cfi directives, use an awk
script to insert them in the right places during the build process, so
GDB can keep track of where the current stack frame is relative to the
stack pointer. This means GDB can produce beautiful stack traces at
any given point when single-stepping through asm functions.

Additionally, when registers are saved on the stack and later
overwritten, emit ..cfi directives so GDB will know where they were
saved relative to the stack pointer. This way, when you look back up
the stack from within an asm function, you can still reliably print
the values of local variables in the caller.

If this awk script were to understand every possible wild and crazy
contortion that an asm programmer can do with the stack and registers,
and always emit the exact ..cfi directives needed for GDB to know what
the register values were in the preceding stack frame, it would
necessarily be as complex as a full x86 emulator. That way lies
madness.

Hence, we assume that the stack pointer will _only_ ever be adjusted
using push/pop or else add/sub with a constant. We do not attempt to
detect every possible way that a register value could be saved for
later use, just the simple and common ways.

Thanks to Szabolcs Nagy for suggesting numerous improvements to this
code.
2015-08-26 14:55:13 +00:00
..
add-cfi.i386.awk Build process uses script to add CFI directives to x86 asm 2015-08-26 14:55:13 +00:00
install.sh fix system breakage window during make install due to permissions 2014-01-15 22:29:13 -05:00
ld.musl-clang.in add musl-clang, a wrapper for system clang installs 2015-07-06 23:52:16 +00:00
mkalltypes.sed refactor headers, especially alltypes.h, and improve C++ ABI compat 2013-07-22 11:22:36 -04:00
musl-clang.in add musl-clang, a wrapper for system clang installs 2015-07-06 23:52:16 +00:00
musl-gcc.specs.sh fix mixup in previous change to gcc wrapper 2013-06-07 10:18:07 -04:00
version.sh add infrastructure to record and report the version of libc.so 2013-12-01 17:27:25 -05:00