Re: [PATCH v2] perf symbols: Consolidate symbol fixup issue

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

Leo Yan wrote:
> After copying Arm64's perf archive with object files and perf.data file
> to x86 laptop, the x86's perf kernel symbol resolution fails.  It
> outputs 'unknown' for all symbols parsing.
> 
> This issue is root caused by the function elf__needs_adjust_symbols(),
> x86 perf tool uses one weak version, Arm64 (and powerpc) has rewritten
> their own version.  elf__needs_adjust_symbols() decides if need to parse
> symbols with the relative offset address; but x86 building uses the weak
> function which misses to check for the elf type 'ET_DYN', so that it
> cannot parse symbols in Arm DSOs due to the wrong result from
> elf__needs_adjust_symbols().
> 
> The DSO parsing should not depend on any specific architecture perf
> building; e.g. x86 perf tool can parse Arm and Arm64 DSOs, vice versa.
> So this patch changes elf__needs_adjust_symbols() as a common function
> and removes the arch specific functions for Arm64 and powerpc.
> 
> In the common elf__needs_adjust_symbols(), it checks elf header and if
> the machine type is one of Arm64/ppc/ppc64, it checks extra condition
> for 'ET_DYN'.  Finally, the Arm64 DSO can be parsed properly with x86's
> perf tool.
> 
> Before:
> 
>   # perf script
>   main  3258          1          branches:                 0 [unknown] ([unknown]) => ffff800010c4665c [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c46670 [unknown] ([kernel.kallsyms]) => ffff800010c4eaec [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eaec [unknown] ([kernel.kallsyms]) => ffff800010c4eb00 [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eb08 [unknown] ([kernel.kallsyms]) => ffff800010c4e780 [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4e7a0 [unknown] ([kernel.kallsyms]) => ffff800010c4eeac [unknown] ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eebc [unknown] ([kernel.kallsyms]) => ffff800010c4ed80 [unknown] ([kernel.kallsyms])
> 
> After:
> 
>   # perf script
>   main  3258          1          branches:                 0 [unknown] ([unknown]) => ffff800010c4665c coresight_timeout+0x54 ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c46670 coresight_timeout+0x68 ([kernel.kallsyms]) => ffff800010c4eaec etm4_enable_hw+0x3cc ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eaec etm4_enable_hw+0x3cc ([kernel.kallsyms]) => ffff800010c4eb00 etm4_enable_hw+0x3e0 ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eb08 etm4_enable_hw+0x3e8 ([kernel.kallsyms]) => ffff800010c4e780 etm4_enable_hw+0x60 ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4e7a0 etm4_enable_hw+0x80 ([kernel.kallsyms]) => ffff800010c4eeac etm4_enable+0x2d4 ([kernel.kallsyms])
>   main  3258          1          branches:  ffff800010c4eebc etm4_enable+0x2e4 ([kernel.kallsyms]) => ffff800010c4ed80 etm4_enable+0x1a8 ([kernel.kallsyms])
> 

I am not able to reproduce this since powerpc64 kernels are not being 
built as ET_EXEC anymore.

> v2: Fixed Arm64 and powerpc native building.
> 
> Reported-by: Mike Leach <mike.leach@linaro.org>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
>  tools/perf/arch/arm64/util/Build            |  1 -
>  tools/perf/arch/arm64/util/sym-handling.c   | 19 -------------------
>  tools/perf/arch/powerpc/util/Build          |  1 -
>  tools/perf/arch/powerpc/util/sym-handling.c | 10 ----------
>  tools/perf/util/symbol-elf.c                |  8 +++++++-
>  5 files changed, 7 insertions(+), 32 deletions(-)
>  delete mode 100644 tools/perf/arch/arm64/util/sym-handling.c
> 
> diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build
> index 0a7782c61209..789956f76d85 100644
> --- a/tools/perf/arch/arm64/util/Build
> +++ b/tools/perf/arch/arm64/util/Build
> @@ -1,6 +1,5 @@
>  perf-y += header.o
>  perf-y += perf_regs.o
> -perf-y += sym-handling.o
>  perf-$(CONFIG_DWARF)     += dwarf-regs.o
>  perf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
>  perf-$(CONFIG_LIBDW_DWARF_UNWIND) += unwind-libdw.o
> diff --git a/tools/perf/arch/arm64/util/sym-handling.c b/tools/perf/arch/arm64/util/sym-handling.c
> deleted file mode 100644
> index 8dfa3e5229f1..000000000000
> --- a/tools/perf/arch/arm64/util/sym-handling.c
> +++ /dev/null
> @@ -1,19 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-only
> -/*
> - *
> - * Copyright (C) 2015 Naveen N. Rao, IBM Corporation
> - */
> -
> -#include "symbol.h" // for the elf__needs_adjust_symbols() prototype
> -#include <stdbool.h>
> -
> -#ifdef HAVE_LIBELF_SUPPORT
> -#include <gelf.h>
> -
> -bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
> -{
> -	return ehdr.e_type == ET_EXEC ||
> -	       ehdr.e_type == ET_REL ||
> -	       ehdr.e_type == ET_DYN;
> -}
> -#endif
> diff --git a/tools/perf/arch/powerpc/util/Build b/tools/perf/arch/powerpc/util/Build
> index 7cf0b8803097..e5c9504f8586 100644
> --- a/tools/perf/arch/powerpc/util/Build
> +++ b/tools/perf/arch/powerpc/util/Build
> @@ -1,5 +1,4 @@
>  perf-y += header.o
> -perf-y += sym-handling.o
>  perf-y += kvm-stat.o
>  perf-y += perf_regs.o
>  perf-y += mem-events.o
> diff --git a/tools/perf/arch/powerpc/util/sym-handling.c b/tools/perf/arch/powerpc/util/sym-handling.c
> index abb7a12d8f93..0856b32f9e08 100644
> --- a/tools/perf/arch/powerpc/util/sym-handling.c
> +++ b/tools/perf/arch/powerpc/util/sym-handling.c
> @@ -10,16 +10,6 @@
>  #include "probe-event.h"
>  #include "probe-file.h"
> 
> -#ifdef HAVE_LIBELF_SUPPORT
> -bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
> -{
> -	return ehdr.e_type == ET_EXEC ||
> -	       ehdr.e_type == ET_REL ||
> -	       ehdr.e_type == ET_DYN;
> -}
> -
> -#endif
> -
>  int arch__choose_best_symbol(struct symbol *syma,
>  			     struct symbol *symb __maybe_unused)
>  {
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 1965aefccb02..ee788ac67415 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -704,8 +704,14 @@ void symsrc__destroy(struct symsrc *ss)
>  	close(ss->fd);
>  }
> 
> -bool __weak elf__needs_adjust_symbols(GElf_Ehdr ehdr)
> +bool elf__needs_adjust_symbols(GElf_Ehdr ehdr)
>  {
> +	if (ehdr.e_machine == EM_AARCH64 ||
> +	    ehdr.e_machine == EM_PPC ||
> +	    ehdr.e_machine == EM_PPC64)
> +		return ehdr.e_type == ET_EXEC || ehdr.e_type == ET_REL ||
> +		       ehdr.e_type == ET_DYN;
> +
>  	return ehdr.e_type == ET_EXEC || ehdr.e_type == ET_REL;

Patch looks good to me. However:

This is only used for checking kernel, so I wonder if we can simply 
include check for ET_DYN across all architectures? This would only 
matter if there are architectures building their kernel as ET_DYN that 
_don't_ want to adjust symbols.


- Naveen