[llvm-dev] Function start address

Muhui Jiang via llvm-dev llvm-dev at lists.llvm.org
Sat Jun 2 23:54:41 PDT 2018


I tried to grep the "DW_TAG_subprogram" from the debug_info . However, I
noticed that the number I found is still less than the whole functions I
found with LLVM IR. Do you have any experiences? Many Thanks


2018-06-02 13:34 GMT+08:00 Muhui Jiang <jiangmuhui at gmail.com>:

> Hi
> Actually, No particular reason. I just think this might be a solution,
> then I use think kind of method. Querying the symbol table would be a good
> choice, but I prefer to use LLVM and dwarf information. I am sorry that I
> am not familiar with debug_info. But thanks to your suggestions. I would
> like to try to solve it with debug_info. It seems work according to your
> comments
> By the way, I am still curious about the reason, why dwarf line mapping
> table would lost so many function's start addresses' information. It would
> be great if you have any comments on this problem. Many Thanks
> Regards
> Muhui
> 2018-06-01 23:00 GMT+08:00 David Blaikie <dblaikie at gmail.com>:
>> Any particular reason you're using debug info to achieve this (& if you
>> are, why you're using the line table?)? You could query the
>> object/executable file's symbol table to find all the functions in an
>> object or executable, and the instruction/address they start at. Or, if you
>> are using debug info for some reason, you could look in the debug_info
>> rather than the line table, and find the DW_TAG_subprogram for each
>> function and look at its low_pc.
>> On Fri, Jun 1, 2018 at 3:36 AM Muhui Jiang via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>> Hi
>>> I am using LLVM Pass combined with dwarf debug information to get all
>>> the function's start address. My steps are below:
>>> First, I write the function pass to get the start line of each function,
>>> which is finished.
>>> Then, based on the start line of every single function, I try to query
>>> the specific line from the dwarf's line binary table, which is generated
>>> with llvm-dwarfdump -debug-line.
>>> However, About one third of the whole functions' start line is not found
>>> in the mapping table. Thus, I can not get the start binary address. I know
>>> that the mapping between source locations and binary addresses is not
>>> bijective. I am using O1 optimization option. I know that some of the
>>> information might be lost legitimately because of optimization. But I don't
>>> think dwarf will miss so many functions' start addresses. Am I right? Any
>>> useful comments and suggestions are welcomed. Many Thanks
>>> Regards
>>> Muhui
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
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