llvm dev - Feb 2010 - [LLVMdev] how to build eglibc using llvm-gcc without unsupported -fno-toplevel-reorder

Hi,

Are there any existing patches (or instructions) for eglibc(may be
glibc/uclibc) to build it correctly with llvm-gcc?
Could you please point to them?

I'm cross-compiling eglibc for new processor using llvm-gcc.
Build passes, but creates mis-optimized crt* files due to lack of
-fno-toplevel-reorder support.
Seems there are reasons to skip support of this option in llvm.
http://www.llvm.org/bugs/show_bug.cgi?id=6364

Particular issue is with libc/sysdeps/generic/initfini.c file which
contains inlined asm with special markup. C is compiled into
asm and then gawk is used to strip different parts for different crt* files.

However, llvm outputs all top level inlined asm first, and only after it
outputs code for functions. As result
gawk strips wrong parts into crt*.s.

Exmple initfini.c fragment:
 asm (".section " ".init" );

 extern void __attribute__ ((section (".init"))) _init (void);
 void
 _init (void)
 {
  call_gmon_start ();

  asm ("ALIGN");
  asm("END_INIT");

  asm ("\n/*@_init_PROLOG_ENDS*/");
  asm ("\n/*@_init_EPILOG_BEGINS*/");
  asm (".section " ".init" );
 }
 asm ("END_INIT");
 asm ("\n/*@_init_EPILOG_ENDS*/");
 asm ("\n/*@_fini_PROLOG_BEGINS*/");


Regards,
Sergey Yakoushkin
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I haven't looked at the code, but why can't you split the .c files
into multiple files instead of splitting the generated asm? Not
running gawk on produced assembly should be a nice cleanup anyway.

Cheers,
-- 
Rafael Ávila de Espíndola

Hi, Rafael

Inlined asm markup inside functions and on the top level is used to split
asm prologue/epilogue parts in very fine-grained manner.
So, splitting source c won't give the same result.

Regards,
Sergey Y.

2010/2/22 Rafael Espindola <espindola at google.com>

I haven't looked at the code, but why can't you split the .c
files
> into multiple files instead of splitting the generated asm? Not
> running gawk on produced assembly should be a nice cleanup anyway.
>
> Cheers,
> --
> Rafael Ávila de Espíndola
>
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On 2010-02-21 23:36, Sergey Yakoushkin wrote:
> Hi, Rafael
> 
> Inlined asm markup inside functions and on the top level is used to
> split asm prologue/epilogue parts in very fine-grained manner.
> So, splitting source c won't give the same result.
You could have 2 files:
 - 1 which contains the function, and a marker where prolog ends
(beginning of file is implicit marker of where it begins)
 - 1 which contains the function, and a marker where epilog begins
(end of file is implicit marker of where it ends)

Or just look at ./sysdeps/x86_64/elf/initfini.c, its a single asm()
block containing all relevant markers, and no C code.
I think thats better than all these hacks to get the asm you want out of
C code.

Best regards,
--Edwin