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kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG is enabled

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Merge module sections only when using Clang LTO. With ld.bfd, merging
sections does not appear to update the symbol tables for the module,
e.g. 'readelf -s' shows the value that a symbol would have had, if
sections were not merged. ld.lld does not show this problem.

The stale symbol table breaks gdb's function disassembler, and presumably
other things, e.g.

  gdb -batch -ex "file arch/x86/kvm/kvm.ko" -ex "disassemble kvm_init"

reads the wrong bytes and dumps garbage.

Fixes: dd2776222abb ("kbuild: lto: merge module sections")
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210322234438.502582-1-seanjc@google.com
This commit is contained in:
Sean Christopherson 2021-03-22 16:44:38 -07:00 committed by Kees Cook
parent a5e13c6df0
commit 6a3193cdd5
1 changed files with 2 additions and 0 deletions
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2
scripts/module.lds.S
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@ -20,6 +20,7 @@ SECTIONS {
__patchable_function_entries : { *(__patchable_function_entries) }
#ifdef CONFIG_LTO_CLANG
/*
* With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and
* -ffunction-sections, which increases the size of the final module.
@ -41,6 +42,7 @@ SECTIONS {
}
.text : { *(.text .text.[0-9a-zA-Z_]*) }
#endif
}
/* bring in arch-specific sections */