[dwarves,v4,2/5] btf_encoder: Do not use both structs and pointers for the same data

Commit Message

Giuliano Procida Feb. 17, 2021, 11:08 a.m. UTC

Many operations in the libelf API return a pointer to a user-provided
struct (on success) or NULL (on failure).

There are a couple of places in btf_elf__write where both structs and
pointers to the same structs are used. Holding on to the pointers
raises ownership and lifetime issues unnecessarily and the code is
cleaner with only a single access path for these data.

The code now treats the returned pointers as booleans.

Acked-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Giuliano Procida <[e-mail]>
---
 libbtf.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

Patch

diff --git a/libbtf.c b/libbtf.c
index 7bc49ba..ace8896 100644
--- a/libbtf.c
+++ b/libbtf.c
@@ -698,8 +698,7 @@  int32_t btf_elf__add_datasec_type(struct btf_elf *btfe, const char *section_name
 
 static int btf_elf__write(const char *filename, struct btf *btf)
 {
-	GElf_Shdr shdr_mem, *shdr;
-	GElf_Ehdr ehdr_mem, *ehdr;
+	GElf_Ehdr ehdr;
 	Elf_Data *btf_data = NULL;
 	Elf_Scn *scn = NULL;
 	Elf *elf = NULL;
@@ -727,13 +726,12 @@  static int btf_elf__write(const char *filename, struct btf *btf)
 
 	elf_flagelf(elf, ELF_C_SET, ELF_F_DIRTY);
 
-	ehdr = gelf_getehdr(elf, &ehdr_mem);
-	if (ehdr == NULL) {
+	if (!gelf_getehdr(elf, &ehdr)) {
 		elf_error("elf_getehdr failed");
 		goto out;
 	}
 
-	switch (ehdr_mem.e_ident[EI_DATA]) {
+	switch (ehdr.e_ident[EI_DATA]) {
 	case ELFDATA2LSB:
 		btf__set_endianness(btf, BTF_LITTLE_ENDIAN);
 		break;
@@ -751,10 +749,10 @@  static int btf_elf__write(const char *filename, struct btf *btf)
 
 	elf_getshdrstrndx(elf, &strndx);
 	while ((scn = elf_nextscn(elf, scn)) != NULL) {
-		shdr = gelf_getshdr(scn, &shdr_mem);
-		if (shdr == NULL)
+		GElf_Shdr shdr;
+		if (!gelf_getshdr(scn, &shdr))
 			continue;
-		char *secname = elf_strptr(elf, strndx, shdr->sh_name);
+		char *secname = elf_strptr(elf, strndx, shdr.sh_name);
 		if (strcmp(secname, ".BTF") == 0) {
 			btf_data = elf_getdata(scn, btf_data);
 			break;