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bpf: Factor out stack_map build ID helpers

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Factor out helpers from stack_map_get_build_id_offset() in
preparation for adding a sleepable build ID resolution path:
stack_map_build_id_set_ip(), stack_map_build_id_offset(), and
stack_map_build_id_set_valid().

While here, refactor stack_map_get_build_id_offset():
  * use continue-driven control flow in the main loop and remove
    build_id_valid label
  * update prev_vma and prev_build_id on the fall-back-to-IP branch so
    the cache reflects the actual VMA seen on the previous IP [1]
  * guard fetch_build_id() with vma_is_anonymous() [2] to skip parse
    attempts that would otherwise fail the ELF magic check

[1] https://lore.kernel.org/bpf/CAEf4Bzac9uWWqBvzH0iFzKvJcq3vxscZ3pKm0sUHmN-F-z9wVQ@mail.gmail.com/
[2] https://lore.kernel.org/bpf/226398c1ff3f2b686c0aeb010408d85fb15df13f9ff60a045bee31e79b9e41e9@mail.kernel.org/

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
Link: https://lore.kernel.org/bpf/20260525223948.1920986-2-ihor.solodrai@linux.dev
This commit is contained in:
Ihor Solodrai 2026-05-25 15:39:46 -07:00 committed by Andrii Nakryiko
parent a4a5d4ee06
commit fc99547a8b
1 changed files with 43 additions and 20 deletions
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63
kernel/bpf/stackmap.c
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@ -152,6 +152,28 @@ static int fetch_build_id(struct vm_area_struct *vma, unsigned char *build_id, b
: build_id_parse_nofault(vma, build_id, NULL);
}
static inline void stack_map_build_id_set_ip(struct bpf_stack_build_id *id)
{
id->status = BPF_STACK_BUILD_ID_IP;
memset(id->build_id, 0, BUILD_ID_SIZE_MAX);
}
static inline u64 stack_map_build_id_offset(unsigned long vm_pgoff,
unsigned long vm_start, u64 ip)
{
return (vm_pgoff << PAGE_SHIFT) + ip - vm_start;
}
static inline void stack_map_build_id_set_valid(struct bpf_stack_build_id *id,
u64 offset,
const unsigned char *build_id)
{
id->status = BPF_STACK_BUILD_ID_VALID;
id->offset = offset;
if (id->build_id != build_id)
memcpy(id->build_id, build_id, BUILD_ID_SIZE_MAX);
}
/*
* Expects all id_offs[i].ip values to be set to correct initial IPs.
* They will be subsequently:
@ -165,44 +187,45 @@ static int fetch_build_id(struct vm_area_struct *vma, unsigned char *build_id, b
static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
u32 trace_nr, bool user, bool may_fault)
{
int i;
struct mmap_unlock_irq_work *work = NULL;
bool irq_work_busy = bpf_mmap_unlock_get_irq_work(&work);
bool has_user_ctx = user && current && current->mm;
struct vm_area_struct *vma, *prev_vma = NULL;
const char *prev_build_id;
const unsigned char *prev_build_id = NULL;
int i;
/* If the irq_work is in use, fall back to report ips. Same
* fallback is used for kernel stack (!user) on a stackmap with
* build_id.
*/
if (!user || !current || !current->mm || irq_work_busy ||
!mmap_read_trylock(current->mm)) {
if (!has_user_ctx || irq_work_busy || !mmap_read_trylock(current->mm)) {
/* cannot access current->mm, fall back to ips */
for (i = 0; i < trace_nr; i++) {
id_offs[i].status = BPF_STACK_BUILD_ID_IP;
memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
}
for (i = 0; i < trace_nr; i++)
stack_map_build_id_set_ip(&id_offs[i]);
return;
}
for (i = 0; i < trace_nr; i++) {
u64 ip = READ_ONCE(id_offs[i].ip);
u64 offset;
if (range_in_vma(prev_vma, ip, ip)) {
if (prev_build_id && range_in_vma(prev_vma, ip, ip)) {
vma = prev_vma;
memcpy(id_offs[i].build_id, prev_build_id, BUILD_ID_SIZE_MAX);
goto build_id_valid;
}
vma = find_vma(current->mm, ip);
if (!vma || fetch_build_id(vma, id_offs[i].build_id, may_fault)) {
/* per entry fall back to ips */
id_offs[i].status = BPF_STACK_BUILD_ID_IP;
memset(id_offs[i].build_id, 0, BUILD_ID_SIZE_MAX);
offset = stack_map_build_id_offset(vma->vm_pgoff, vma->vm_start, ip);
stack_map_build_id_set_valid(&id_offs[i], offset, prev_build_id);
continue;
}
build_id_valid:
id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ip - vma->vm_start;
id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
vma = find_vma(current->mm, ip);
if (!vma || vma_is_anonymous(vma) ||
fetch_build_id(vma, id_offs[i].build_id, may_fault)) {
/* per entry fall back to ips */
stack_map_build_id_set_ip(&id_offs[i]);
prev_vma = vma;
prev_build_id = NULL;
continue;
}
offset = stack_map_build_id_offset(vma->vm_pgoff, vma->vm_start, ip);
stack_map_build_id_set_valid(&id_offs[i], offset, id_offs[i].build_id);
prev_vma = vma;
prev_build_id = id_offs[i].build_id;
}