[llvm-commits] PCH fix

Tanya M. Lattner tonic at nondot.org
Thu May 17 11:08:48 PDT 2007

> This patch is good. I installed this patch in mainline sources. I agree, this 
> should also go in 2.0 release branch.

Devang - Can you please apply this patch to the release-2.0 branch? Also, 
it would be great if we could push this to the mirror ASAP, so I can begin 
making new tarballs tonight. I think Bill might be able to do that if you 



> Thanks Anton for taking care of this bug.
> -
> Devang
> On May 17, 2007, at 2:53 AM, Anton Korobeynikov wrote:
>>  Hello, Everyone.
>>  Attached patch fixes PCHs for both TOT and 2.0 release.
>>  There were 2 problems:
>>  1. flush() method of oFILEstream doesn't actually flush the file. This
>>  can lead to incorrect offsets calculations in the PCH handling code and
>>  junk output. This problem seems to be highly platform-dependent: it
>>  fails for linux & mingw32, but passes for darwin.
>>  There are two possible solutions: either use stdio_sync_buf for
>>  oFILEstream or flush the asm_out_file by hands. I preferred second.
>>  2. This problem is not platform specific. We have the following sequence
>>  of calls during PCH's read:
>>   1) llvm_start_asm_file()
>>   2) llvm_read_pch()
>>   3) llvm_end_asm_file()
>>  In llvm_start_asm_file() routine 2 FunctionPassManagers
>>  (PerFunctionPasses and CodeGenPasses) are created having TheModule used
>>  during construction, later in the llvm_read_pch() TheModule is freed and
>>  recreated, but ... PassManagers still holds pointer to old module. This
>>  causes uninitialised memory reads (and segfaults later) during
>>  doFinalization() calls in the llvm_end_asm_file().
>>  The solutions was: factor out passmanagers' creation code to separate
>>  routine and call it in llvm_read_pch() in order to recreate passes.
>>  I think, this patch should be propagated to 2.0 release branch, or,
>>  otherwise PCHs should be marked as "broken in 2.0".
>>  Patch tested with Qt compilation on x86/linux.
>>  <pch_fix.diff>

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