Re: [PATCH v2 3/3] Make exec-file-mismatch compare build IDs

[Pedro Alves <palves@redhat.com>]

On 5/21/20 2:32 PM, Philippe Waroquiers wrote:

> Comparing build-id introduced a change of behaviour when GDB has
> loaded a file, and the user recompiles this file followed by an attach.
> 
> Before this patch, when GDB had a file loaded and the user recompiled
> the file and attached to a process using this recompiled file,
> GDB used to reload the file automatically.
> Now, GDB reports a mismatch, indicating  a "mismatch"
> instead of automatically re-loading the new file version.
> 
> Technically, GDB mismatch is correct, but I am wondering if this change
> of behaviour is desirable.  At least, it introduces a difference
> of behaviour between run (that will just indicate the file has changed
> and reload automatically) and attach (that will warn and ask).
> 
> 
>  (gdb) atta 10615
> Attaching to program: /bd/home/philippe/gdb/git/build_moreaa/gdb/gdb, process 10615
> [New LWP 10616]
> [New LWP 10617]
> [New LWP 10618]
> [New LWP 10620]
> [New LWP 10621]
> [New LWP 10622]
> [New LWP 10623]
> warning: Mismatch between current exec-file /bd/home/philippe/gdb/git/build_moreaa/gdb/gdb
> and automatically determined exec-file /bd/home/philippe/gdb/git/build_moreaa/gdb/gdb
> exec-file-mismatch handling is currently "ask"
> Load new symbol table from "/bd/home/philippe/gdb/git/build_moreaa/gdb/gdb"? (y or n) 
> 
> 
> while previously, GDB was doing:
> (gdb) atta 14099
> Attaching to program: /bd/home/philippe/gdb/git/build_moreaa/gdb/gdb, process 14099
> [New LWP 14100]
> [New LWP 14101]
> [New LWP 14102]
> [New LWP 14104]
> [New LWP 14105]
> [New LWP 14106]
> [New LWP 14107]
> `/bd/home/philippe/gdb/git/build_moreaa/gdb/gdb' has changed; re-reading symbols.

It looks to me like GDB is doing the validation too soon.  It should figure out
that the local file changed, and thus reload it (the "re-reading symbols"), and only
after, should it do validation?  After re-reading, the build ids should match again.
Or do the "has changed, re-reading" thing earlier, but not sure that's practical.

Thanks,
Pedro Alves