[PATCH v3] libbpf: Fix determine_ptr_size() guessing

[PATCH v3] libbpf: Fix determine_ptr_size() guessing

[Douglas RAILLARD]

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

Re: [PATCH v3] libbpf: Fix determine_ptr_size() guessing

[patchwork-bot+netdevbpf]

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!
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