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bff60150f7
As gcc doc [1] shows:
Most optimizations are completely disabled at -O0 or if an -O level is
not set on the command line, even if individual optimization flags are
specified.
Test result [2] shows, gcc>=11.1.0 deviates from the above description,
but before gcc 11.1.0, "-O0" still forcely uses frame pointer in the
_start function even if the individual optimize("omit-frame-pointer")
flag is specified.
The frame pointer related operations will change the stack pointer (e.g.
In x86_64, an extra "push %rbp" will be inserted at the beginning of
_start) and make it differs from the one we expected, as a result, break
the whole startup function.
To fix up this issue, as suggested by Thomas, the individual "Os" and
"omit-frame-pointer" optimize flags are used together on _start function
to disable frame pointer completely even if the -O0 is set on the
command line.
[1]: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html
[2]: https://lore.kernel.org/lkml/20230714094723.140603-1-falcon@tinylab.org/
Suggested-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/lkml/34b21ba5-7b59-4b3b-9ed6-ef9a3a5e06f7@t-8ch.de/
Fixes:
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| .. | ||
| .gitignore | ||
| arch-aarch64.h | ||
| arch-arm.h | ||
| arch-i386.h | ||
| arch-loongarch.h | ||
| arch-mips.h | ||
| arch-riscv.h | ||
| arch-s390.h | ||
| arch-x86_64.h | ||
| arch.h | ||
| compiler.h | ||
| ctype.h | ||
| errno.h | ||
| Makefile | ||
| nolibc.h | ||
| signal.h | ||
| stackprotector.h | ||
| std.h | ||
| stdint.h | ||
| stdio.h | ||
| stdlib.h | ||
| string.h | ||
| sys.h | ||
| time.h | ||
| types.h | ||
| unistd.h | ||