| Message ID | 20221117181308.1761316-1-adhemerval.zanella@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] i386: Avoid avoid rely on linker optimization to avoid relocation | expand |
On Thu, Nov 17, 2022 at 10:13 AM Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote: > > lld does not implement all the linker optimization to avoid the GOT > relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc). > The current 'movl main@GOT(%ebx), %eax' will then create a GOT > relocation when building with lld, which make static-pie status to > not being able to start the provided main function. > > The change uses a __wrap_main local symbol, which in turn calls main > (similar as used by aarch64 and s390x). > > Checked on i686-linux-gnu with binutils and lld. > --- > sysdeps/i386/start.S | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S > index 4ec04bdfd7..23e4f2b012 100644 > --- a/sysdeps/i386/start.S > +++ b/sysdeps/i386/start.S > @@ -98,11 +98,10 @@ ENTRY (_start) > pushl main@GOT(%ebx) > # else > /* Avoid relocation in static PIE since _start is called before > - it is relocated. Don't use "leal main@GOTOFF(%ebx), %eax" > - since main may be in a shared object. Linker will convert > - "movl main@GOT(%ebx), %eax" to "leal main@GOTOFF(%ebx), %eax" > + it is relocated. This also avoid rely on linker optimization to > + transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)' > if main is defined locally. */ > - movl main@GOT(%ebx), %eax > + leal __wrap_main@GOTOFF(%ebx), %eax > pushl %eax > # endif > > @@ -130,6 +129,12 @@ ENTRY (_start) > 1: movl (%esp), %ebx > ret > #endif > + > +#if defined PIC && !defined SHARED > +__wrap_main: > + _CET_ENDBR > + jmp main@PLT > +#endif > END (_start) > > /* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so > -- > 2.34.1 > LGTM. Thanks.
On 2022-11-17, H.J. Lu wrote: >On Thu, Nov 17, 2022 at 10:13 AM Adhemerval Zanella ><adhemerval.zanella@linaro.org> wrote: >> >> lld does not implement all the linker optimization to avoid the GOT >> relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc). >> The current 'movl main@GOT(%ebx), %eax' will then create a GOT >> relocation when building with lld, which make static-pie status to >> not being able to start the provided main function. >> >> The change uses a __wrap_main local symbol, which in turn calls main >> (similar as used by aarch64 and s390x). >> >> Checked on i686-linux-gnu with binutils and lld. >> --- >> sysdeps/i386/start.S | 13 +++++++++---- >> 1 file changed, 9 insertions(+), 4 deletions(-) >> >> diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S >> index 4ec04bdfd7..23e4f2b012 100644 >> --- a/sysdeps/i386/start.S >> +++ b/sysdeps/i386/start.S >> @@ -98,11 +98,10 @@ ENTRY (_start) >> pushl main@GOT(%ebx) >> # else >> /* Avoid relocation in static PIE since _start is called before >> - it is relocated. Don't use "leal main@GOTOFF(%ebx), %eax" >> - since main may be in a shared object. Linker will convert >> - "movl main@GOT(%ebx), %eax" to "leal main@GOTOFF(%ebx), %eax" >> + it is relocated. This also avoid rely on linker optimization to >> + transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)' >> if main is defined locally. */ >> - movl main@GOT(%ebx), %eax >> + leal __wrap_main@GOTOFF(%ebx), %eax >> pushl %eax >> # endif >> >> @@ -130,6 +129,12 @@ ENTRY (_start) >> 1: movl (%esp), %ebx >> ret >> #endif >> + >> +#if defined PIC && !defined SHARED >> +__wrap_main: >> + _CET_ENDBR >> + jmp main@PLT >> +#endif >> END (_start) >> >> /* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so >> -- >> 2.34.1 >> > >LGTM. > >Thanks. LGTM, too. Reviewed-by: Fangrui Song <maskray@google.com> BTW: do you know when start.o/start.os is assembled without -DPIC? I find that in both --enable-static-pie and --disable-static-pie modes, both start.o and start.os use -DPIC. start.os uses an additional -DSHARED. Is the non-`#ifdef __PIC__` path dead?
diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S index 4ec04bdfd7..23e4f2b012 100644 --- a/sysdeps/i386/start.S +++ b/sysdeps/i386/start.S @@ -98,11 +98,10 @@ ENTRY (_start) pushl main@GOT(%ebx) # else /* Avoid relocation in static PIE since _start is called before - it is relocated. Don't use "leal main@GOTOFF(%ebx), %eax" - since main may be in a shared object. Linker will convert - "movl main@GOT(%ebx), %eax" to "leal main@GOTOFF(%ebx), %eax" + it is relocated. This also avoid rely on linker optimization to + transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)' if main is defined locally. */ - movl main@GOT(%ebx), %eax + leal __wrap_main@GOTOFF(%ebx), %eax pushl %eax # endif @@ -130,6 +129,12 @@ ENTRY (_start) 1: movl (%esp), %ebx ret #endif + +#if defined PIC && !defined SHARED +__wrap_main: + _CET_ENDBR + jmp main@PLT +#endif END (_start) /* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so