Re: [PATCH] perf callchain: Handle multiple address spaces

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Tue, Apr 14, 2026 at 02:42:41PM +0200, Thomas Richter wrote:
> perf test 'perf inject to convert DWARF callchains to regular ones'
> fails on s390. It was introduced with
> commit 92ea788d2af4 ("perf inject: Add --convert-callchain option")
> 
> The failure comes the difference in output. Without the inject script to
> convert DWARF the callchains is:
>  # ./perf record -F 999 --call-graph dwarf -- perf test -w noploop
>  # ./perf report -i perf.data --stdio --no-children -q \
> 					 --percent-limit=1 > /tmp/111
>  # cat /tmp/111
>     99.30%  perf-noploop  perf               [.] noploop
>             |
>             ---noploop
>                run_workload (inlined)
>                cmd_test
>                run_builtin (inlined)
>                handle_internal_command
>                run_argv (inlined)
>                main
>                __libc_start_call_main
>                __libc_start_main_impl (inlined)
>                _start
>  #
> 
> With the inject script step the output is:
>  # ./perf inject -i perf.data --convert-callchain -o /tmp/perf-inject-1.out
>  # ./perf report -i /tmp/perf-inject-1.out --stdio --no-children -q \
> 		--percent-limit=1 > /tmp/222
>  # cat /tmp/222
>     99.40%  perf-noploop  perf               [.] noploop
>             |
>             ---noploop
>                run_workload (inlined)
>                cmd_test
>                run_builtin (inlined)
>                handle_internal_command
>                run_argv (inlined)
>                main
>                _start
>  # diff /tmp/111 /tmp/222
>  1c1
>  <     99.30%  perf-noploop  perf               [.] noploop
>  ---
>  >     99.40%  perf-noploop  perf               [.] noploop
>  10,11d9
>  <                __libc_start_call_main
>  <                __libc_start_main_impl (inlined)
>  #
> 
> The difference are the symbols __libc_start_call_main and
> __libc_start_main_impl.
> 
> On x86_64, kernel and user space share a single virtual address space,
> with the kernel mapped to the upper end of memory. The instruction
> pointer value alone is sufficient to distinguish between user space
> and kernel space addresses. This is not true for s390, which uses
> separate address spaces for user and kernel. The same virtual address
> can be valid in both address spaces, so the instruction pointer value
> alone cannot determine whether an address belongs to the kernel or
> user space. Instead, perf must rely on the cpumode metadata derived
> from the processor status word (PSW) at sample time.
> 
> In function perf_event__convert_sample_callchain() the first part
> copies a kernel callchain and context entries, if any.
> It then appends additional entries ignoring the address space
> architecture. Taking that into account, the symbols at addresses
> 
>    0x3ff970348cb __libc_start_call_main
>    0x3ff970349c5 __libc_start_main_impl
> 
> (located after the kernel address space on s390) are now included.
> 
> Output before:
>  # ./perf test 83
>  83: perf inject to convert DWARF callchains to regular ones : FAILED!
> 
> Output after:
>  # ./perf test 83
>  83: perf inject to convert DWARF callchains to regular ones : Ok
> 
> Question to Namhyung:
> In function perf_event__convert_sample_callchain() just before the
> for() loop this patch modifies, the kernel callchain is copied,
> see this comment and the next 5 lines:
>    /* copy kernel callchain and context entries */ 
> Then why is machine__kernel_ip() needed in the for() loop, when
> the kernel entries have been copied just before the loop?

IIRC I wanted to make sure to have PERF_CONTEXT_* part in the raw
callchains.

> 
> Note: This patch was tested on x86_64 virtual machine and succeeded.
> 
> Fixes: 92ea788d2af4 ("perf inject: Add --convert-callchain option")
> Cc: Namhyung Kim <namhyung@kernel.org>
> 
> Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>

Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung

> ---
>  tools/perf/arch/common.c    | 4 +++-
>  tools/perf/builtin-inject.c | 3 ++-
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/arch/common.c b/tools/perf/arch/common.c
> index 21836f70f231..ad0cab830a4d 100644
> --- a/tools/perf/arch/common.c
> +++ b/tools/perf/arch/common.c
> @@ -237,5 +237,7 @@ int perf_env__lookup_objdump(struct perf_env *env, char **path)
>   */
>  bool perf_env__single_address_space(struct perf_env *env)
>  {
> -	return strcmp(perf_env__arch(env), "sparc");
> +	const char *arch = perf_env__arch(env);
> +
> +	return strcmp(arch, "s390") && strcmp(arch, "sparc");
>  }
> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> index f174bc69cec4..6ab20df358c4 100644
> --- a/tools/perf/builtin-inject.c
> +++ b/tools/perf/builtin-inject.c
> @@ -438,7 +438,8 @@ static int perf_event__convert_sample_callchain(const struct perf_tool *tool,
>  
>  	node = cursor->first;
>  	for (k = 0; k < cursor->nr && i < PERF_MAX_STACK_DEPTH; k++) {
> -		if (machine__kernel_ip(machine, node->ip))
> +		if (machine->single_address_space &&
> +		    machine__kernel_ip(machine, node->ip))
>  			/* kernel IPs were added already */;
>  		else if (node->ms.sym && node->ms.sym->inlined)
>  			/* we can't handle inlined callchains */;
> -- 
> 2.53.0
>