[Bug breakpoints/26096] gdb sets breakpoint at cold clone

["bernd.edlinger at hotmail dot de" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=26096

Bernd Edlinger <bernd.edlinger at hotmail dot de> changed:

           What    |Removed                     |Added
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                 CC|                            |bernd.edlinger at hotmail dot de

--- Comment #6 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Tom de Vries from comment #3)
> Another thing I noticed with cold clones:
> ...
> $ gdb -q -batch a.out -ex "maint print psymbols" | egrep "foo|bar"
>     `bar', function, 0x400455
>     `foo', function, 0x400450
> ...
> 
> The psymbol address of the function bar is the address of "bar() [clone
> .cold]".
> 
> Presumably we'd want the entry address here.
> 
> Looking at the corresponding DWARF, we have:
> ...
>  <1><990>: Abbrev Number: 35 (DW_TAG_subprogram)
>     <991>   DW_AT_name        : foo
>     <995>   DW_AT_decl_file   : 1
>     <996>   DW_AT_decl_line   : 8
>     <997>   DW_AT_decl_column : 1
>     <998>   DW_AT_type        : <0x39b>
>     <99c>   DW_AT_ranges      : 0x40
>     <9a0>   DW_AT_frame_base  : 1 byte block: 9c       
> (DW_OP_call_frame_cfa)
>     <9a2>   DW_AT_GNU_all_call_sites: 1
>     <9a2>   DW_AT_sibling     : <0x9b4>
> ...
> 
> In DWARF 4 standard 2.18 Entry Address we read:
> ...
> If no DW_AT_entry_pc attribute is present, then the entry address is assumed
> to be the same as the value of the DW_AT_low_pc attribute, if present;
> otherwise, the entry address is unknown.
> ...
> 
> In this case, we have no DW_AT_entry_pc and no DW_AT_low_pc attribute. 
> Arguably, this is a gcc bug.
> 
> Either way, in absence of a fix in gcc for this, we could adapt a
> interpretation that the entry pc is the start address of the first range. At
> least, this works for this exec:
> ...
>     00000070 00000000004005b0 00000000004005d7
>     00000070 0000000000400455 000000000040045a
>     00000070 <End of list>
> ...
> 
> This also seems to be the current interpretation for full symtabs, AFAIU
> from the comment for BLOCK_ENTRY_PC in block.h:
> ...
> /* Define the "entry pc" for a block BL to be the lowest (start) address    
> 
>    for the block when all addresses within the block are contiguous.  If    
> 
>    non-contiguous, then use the start address for the first range in the    
> 
>    block.                                                                   
> 
> ...

This is related to this patch:
https://sourceware.org/pipermail/gdb-patches/2021-May/179369.html

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