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[Tinycc-devel] Fallout from commit 01c041923474750a236da02561f0f88354458

From: Thomas Preud'homme
Subject: [Tinycc-devel] Fallout from commit 01c041923474750a236da02561f0f8835445848b
Date: Tue, 09 Sep 2014 22:17:47 +0800
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Hi Michael,

A recent upload of tcc in Debian showed a self test failure [1] due to a 
failed R_ARM_PC24 relocation. The two bits with the smallest weight are 0 so 
it's a problem of out of range branch.


The biggest change in this code was your commits to get rid of 
runtime_plt_and_got so I took a closer look at it. A few things surprised me 
so I wanted to ask you some questions.

1) You added the support for R_ARM_GLOB_DAT and R_ARM_JUMP_SLOT relocations 
but the computation you added ignore the possible addend at *ptr by doing a 
simple assignment. Is that normal? Did I miss something?

2) When creating a GOT and PLT entry for a R_ARM_PC24, R_ARM_CALL or 
R_ARM_JUMP24 you add the offset of the PLT entry to the place being relocated. 
I'm not sure I got it right but it seems to me that the relocation will be 
processed again in relocate_section and seems the symbol referenced is still 
the target function (and not the PLT entry created) as the index in the r_info 
field of the relocation has remained unchanged. Also this put some relocation 
computation in build_got_entries. Why not change the initial relocation to 
make it resolve to the PLT entry.

3) I don't see any test for the type of output when deciding what type of 
relocation to add. So even when the output is in memory reloc_type will be 
JUMP_SLOT which will lead to a PLT entry being created. This seems to 
contradict the comment near the end of put_got_entry. The comment seems wrong 
as I don't see how a branch could be relocated without a PLT entry.

4) the jump table that was removed in subsequent patch was only available when 
outputing to memory. But now a PLT and GOT entry is created no matter what 
type of output (see 3) above).

Best regards,


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