Re: [PATCH] tools/perf: Fix dso kernel load and symbol process to correctly map dso to its long_name, type and adjust_symbols

[Adrian Hunter <adrian.hunter@intel.com>]

On 11/08/23 08:15, Athira Rajeev wrote:
> Test "object cocde reading" fails sometimes for kernel address
> as below:
> 
>     Reading object code for memory address: 0xc000000000004c3c
>     File is: [kernel.kallsyms]
>     On file address is: 0x14c3c
>     dso__data_read_offset failed
>     test child finished with -1
>     ---- end ----
>     Object code reading: FAILED!
> 
> Here the dso__data_read_offset fails for symbol address
> 0xc000000000004c3c. This is because, the dso long_name here
> is [kernel.kallsyms] and hence open_dso fails to open this
> file. There is an incorrect dso to map handling here. The
> key points here is:
> - dso long_name is set to [kernel.kallsyms]. This file is
>   not present and hence returns error
> - DSO binary type is set to DSO_BINARY_TYPE__NOT_FOUND
> - dso adjust_symbols is set to zero
> 
> In the end dso__data_read_offset() returns -1 and the address
> 0x14c3c can not be resolved. Hence the test fails. But the
> address actually maps to kernel dso
> 
>     # objdump -z -d --start-address=0xc000000000004c3c --stop-address=0xc000000000004cbc /home/athira/linux/vmlinux
> 
>     /home/athira/linux/vmlinux:     file format elf64-powerpcle
> 
>     Disassembly of section .head.text:
> 
>     c000000000004c3c <exc_virt_0x4c00_system_call+0x3c>:
>     c000000000004c3c:	a6 02 9b 7d 	mfsrr1  r12
>     c000000000004c40:	78 13 42 7c 	mr      r2,r2
>     c000000000004c44:	18 00 4d e9 	ld      r10,24(r13)
>     c000000000004c48:	60 c6 4a 61 	ori     r10,r10,50784
>     c000000000004c4c:	a6 03 49 7d 	mtctr   r10
> 
> Fix the dso__process_kernel_symbol function to set the
> binary_type and adjust_symbols. adjust_symbols is used by
> function "map__rip_2objdump" which converts symbol start
> address to objdump address. Also set the dso long_name during
> dso__load_vmlinux function.
> 
> Suggested-by: Adrian Hunter <adrian.hunter@intel.com>
> Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>

Acked-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
> Note: Found similar discussion here in thread:
>       https://www.spinics.net/lists/linux-perf-users/msg06337.html
>       where Adrian proposed the fix, but looks like this was
>       not added to the perf. Hence addeed Suggested-by from Adrian.
> 
>       Additional to the fix proposed by Adrian, the patch also
>       adds setting of adjust_symbols which is needed for
>       map__rip_2objdump to convert symbol start to objdump address.
> 
>  tools/perf/util/symbol-elf.c |  2 ++
>  tools/perf/util/symbol.c     | 15 ++++++++++-----
>  2 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 252d26a59e64..9e7eeaf616b8 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1440,6 +1440,8 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
>  		curr_dso->kernel = dso->kernel;
>  		curr_dso->long_name = dso->long_name;
>  		curr_dso->long_name_len = dso->long_name_len;
> +		curr_dso->binary_type = dso->binary_type;
> +		curr_dso->adjust_symbols = dso->adjust_symbols;
>  		curr_map = map__new2(start, curr_dso);
>  		dso__put(curr_dso);
>  		if (curr_map == NULL)
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index f849f9ef68e6..3f36675b7c8f 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -2204,15 +2204,20 @@ int dso__load_vmlinux(struct dso *dso, struct map *map,
>  	if (symsrc__init(&ss, dso, symfs_vmlinux, symtab_type))
>  		return -1;
>  
> +	/*
> +	 * dso__load_sym() may copy 'dso' which will result in the copies having
> +	 * an incorrect long name unless we set it here first.
> +	 */
> +	dso__set_long_name(dso, vmlinux, vmlinux_allocated);
> +	if (dso->kernel == DSO_SPACE__KERNEL_GUEST)
> +		dso->binary_type = DSO_BINARY_TYPE__GUEST_VMLINUX;
> +	else
> +		dso->binary_type = DSO_BINARY_TYPE__VMLINUX;
> +
>  	err = dso__load_sym(dso, map, &ss, &ss, 0);
>  	symsrc__destroy(&ss);
>  
>  	if (err > 0) {
> -		if (dso->kernel == DSO_SPACE__KERNEL_GUEST)
> -			dso->binary_type = DSO_BINARY_TYPE__GUEST_VMLINUX;
> -		else
> -			dso->binary_type = DSO_BINARY_TYPE__VMLINUX;
> -		dso__set_long_name(dso, vmlinux, vmlinux_allocated);
>  		dso__set_loaded(dso);
>  		pr_debug("Using %s for symbols\n", symfs_vmlinux);
>  	}