Re: [PATCH] PR29997: Fix the symbol aliases search failure when symbol version is missing

[Aaron Merey <amerey@redhat.com>]

Hi Di,

Thanks for working on this.

On Sun, Nov 5, 2023 at 12:00 AM Di Chen via Systemtap
<systemtap@sourceware.org> wrote:
>
> From 9273dc95658b109f048e4ec9b0fcde96e34f3419 Mon Sep 17 00:00:00 2001
> From: Di Chen <dichen@redhat.com>
> Date: Sun, 5 Nov 2023 11:23:50 +0800
> Subject: [PATCH] PR29997: Fix the symbol aliases search failure when symbol
>  version is missing
>
> After calling module_info::update_symtab, function aliases will be
> populated. Then the updated symtab will be used for symbol searching.
>
> For the _IO_new_fopen familty with the aliases:
>
>   $ eu-readelf -s /lib64/libc.so.6  | grep 0000000000077440
>     247: 0000000000077440     14 FUNC    WEAK   DEFAULT       16 fopen64@
> @GLIBC_2.2.5
>    1014: 0000000000077440     14 FUNC    GLOBAL DEFAULT       16 fopen@
> @GLIBC_2.2.5
>    1028: 0000000000077440     14 FUNC    GLOBAL DEFAULT       16 _IO_fopen@
> @GLIBC_2.2.5
>    1556: 0000000000077440     14 FUNC    LOCAL  DEFAULT       16 _IO_fopen64
>    3471: 0000000000077440     14 FUNC    LOCAL  DEFAULT       16 __new_fopen
>    4765: 0000000000077440     14 FUNC    LOCAL  DEFAULT       16
> _IO_new_fopen
>    5110: 0000000000077440     14 FUNC    WEAK   DEFAULT       16 fopen64
>    7198: 0000000000077440     14 FUNC    GLOBAL DEFAULT       16 fopen@
> @GLIBC_2.2.5
>    7433: 0000000000077440     14 FUNC    GLOBAL DEFAULT       16 _IO_fopen@
> @GLIBC_2.2.5
>
>   a) fopen@@GLIBC_2.2.5 exists in the updated symtab
>   b) fopen does not exist in the updated symtab
>
> This PR is to add a version info padding when symbol cannot be found in
> the updated symtab.
>
> Signed-off-by: Di Chen <dichen@redhat.com>
> ---
>  dwflpp.cxx | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/dwflpp.cxx b/dwflpp.cxx
> index a4f66440f..22e1479c9 100644
> --- a/dwflpp.cxx
> +++ b/dwflpp.cxx
> @@ -1052,6 +1052,15 @@ dwflpp::iterate_over_functions<void>(int
> (*callback)(Dwarf_Die*, void*),
>      }
>
>    auto range = v->equal_range(function);
> +  // version info padding if the symbol is not found
> +  if (range.first == range.second)
> +    {
> +    std::string function_with_ver = function + "@";
> +    for (auto it = v->begin(); it != v->end(); ++it)
> +      if (it->first.find(function_with_ver) == 0)
> +        function_with_ver = it->first;
> +    range = v->equal_range(function_with_ver);
> +    }

This fixes the bug for function names without wildcards.  However
the bug can still be reproduced using function names with wildcards.
For example the following command incorrectly returns no results:

  $ stap -L 'process("/lib64/libc.so.6").function("fo*en")'

We'll need additional '@' handling in the section of
dwflpp::iterate_over_functions that matches wildcards.

>    if (range.first != range.second)
>      {
>        for (auto it = range.first; it != range.second; ++it)
> @@ -1138,6 +1147,15 @@ dwflpp::iterate_single_function<void>(int
> (*callback)(Dwarf_Die*, void*),
>      }
>
>    auto range = v->equal_range(function);
> +  // version info padding if the symbol is not found
> +  if (range.first == range.second)
> +    {
> +    std::string function_with_ver = function + "@";
> +    for (auto it = v->begin(); it != v->end(); ++it)
> +      if (it->first.find(function_with_ver) == 0)
> +        function_with_ver = it->first;
> +    range = v->equal_range(function_with_ver);
> +    }
>    if (range.first != range.second)
>      {
>        for (auto it = range.first; it != range.second; ++it)
> --
> 2.41.0

Aaron