* [PATCH v3] libbpf: Fix determine_ptr_size() guessing
@ 2022-05-24 9:44 Douglas RAILLARD
2022-05-31 22:50 ` patchwork-bot+netdevbpf
0 siblings, 1 reply; 2+ messages in thread
From: Douglas RAILLARD @ 2022-05-24 9:44 UTC (permalink / raw)
To: bpf
Cc: beata.michalska, Douglas Raillard, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Martin KaFai Lau, Song Liu,
Yonghong Song, John Fastabend, KP Singh, Nathan Chancellor,
Nick Desaulniers, Tom Rix, netdev, linux-kernel, llvm
From: Douglas Raillard <douglas.raillard@arm.com>
One strategy employed by libbpf to guess the pointer size is by finding
the size of "unsigned long" type. This is achieved by looking for a type
of with the expected name and checking its size.
Unfortunately, the C syntax is friendlier to humans than to computers
as there is some variety in how such a type can be named. Specifically,
gcc and clang do not use the same names for integer types in debug info:
- clang uses "unsigned long"
- gcc uses "long unsigned int"
Lookup all the names for such a type so that libbpf can hope to find the
information it wants.
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>
---
tools/lib/bpf/btf.c | 29 +++++++++++++++++++++--------
1 file changed, 21 insertions(+), 8 deletions(-)
CHANGELOG
v2:
* Added missing case for "long"
v3:
* Refactor a bit to use a table
* Provide the type names used by gcc and clang in commit msg
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 1383e26c5d1f..65c492a6807f 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -470,12 +470,25 @@ const struct btf_type *btf__type_by_id(const struct btf *btf, __u32 type_id)
return btf_type_by_id((struct btf *)btf, type_id);
}
+static const char * const long_aliases[] = {
+ "long",
+ "long int",
+ "int long",
+ "unsigned long",
+ "long unsigned",
+ "unsigned long int",
+ "unsigned int long",
+ "long unsigned int",
+ "long int unsigned",
+ "int unsigned long",
+ "int long unsigned",
+};
+
static int determine_ptr_size(const struct btf *btf)
{
const struct btf_type *t;
const char *name;
- int i, n;
-
+ int i, j, n;
if (btf->base_btf && btf->base_btf->ptr_sz > 0)
return btf->base_btf->ptr_sz;
@@ -489,12 +502,12 @@ static int determine_ptr_size(const struct btf *btf)
if (!name)
continue;
- if (strcmp(name, "long int") == 0 ||
- strcmp(name, "long unsigned int") == 0) {
- if (t->size != 4 && t->size != 8)
- continue;
- return t->size;
- }
+ if (t->size != 4 && t->size != 8)
+ continue;
+
+ for (j = 0; j < ARRAY_SIZE(long_aliases); j++)
+ if (!strcmp(name, long_aliases[j]))
+ return t->size;
}
return -1;
--
2.25.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v3] libbpf: Fix determine_ptr_size() guessing
2022-05-24 9:44 [PATCH v3] libbpf: Fix determine_ptr_size() guessing Douglas RAILLARD
@ 2022-05-31 22:50 ` patchwork-bot+netdevbpf
0 siblings, 0 replies; 2+ messages in thread
From: patchwork-bot+netdevbpf @ 2022-05-31 22:50 UTC (permalink / raw)
To: Douglas RAILLARD
Cc: bpf, beata.michalska, ast, daniel, andrii, kafai, songliubraving,
yhs, john.fastabend, kpsingh, nathan, ndesaulniers, trix, netdev,
linux-kernel, llvm
Hello:
This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:
On Tue, 24 May 2022 10:44:47 +0100 you wrote:
> From: Douglas Raillard <douglas.raillard@arm.com>
>
> One strategy employed by libbpf to guess the pointer size is by finding
> the size of "unsigned long" type. This is achieved by looking for a type
> of with the expected name and checking its size.
>
> Unfortunately, the C syntax is friendlier to humans than to computers
> as there is some variety in how such a type can be named. Specifically,
> gcc and clang do not use the same names for integer types in debug info:
>
> [...]
Here is the summary with links:
- [v3] libbpf: Fix determine_ptr_size() guessing
https://git.kernel.org/bpf/bpf-next/c/8a140f1b12f7
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
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