[PATCH V2 20/20] perf buildid-cache: kcore_copy: Amend the offset of sections that remap kernel text

[Adrian Hunter]

x86 PTI entry trampolines all map to the same physical page. If that is
reflected in the program headers of /proc/kcore, then do the same for the
copy of kcore.

Signed-off-by: Adrian Hunter <adrian.hun...@intel.com>
---
 tools/perf/util/symbol-elf.c | 53 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 584966913aeb..29770ea61768 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1390,6 +1390,7 @@ struct phdr_data {
        u64 addr;
        u64 len;
        struct list_head node;
+       struct phdr_data *remaps;
 };
 
 struct sym_data {
@@ -1597,16 +1598,62 @@ static int kcore_copy__read_maps(struct kcore_copy_info 
*kci, Elf *elf)
        return 0;
 }
 
+static void kcore_copy__find_remaps(struct kcore_copy_info *kci)
+{
+       struct phdr_data *p, *k = NULL;
+       u64 kend;
+
+       if (!kci->stext)
+               return;
+
+       /* Find phdr that corresponds to the kernel map (contains stext) */
+       kcore_copy__for_each_phdr(kci, p) {
+               u64 pend = p->addr + p->len - 1;
+
+               if (p->addr <= kci->stext && pend >= kci->stext) {
+                       k = p;
+                       break;
+               }
+       }
+
+       if (!k)
+               return;
+
+       kend = k->offset + k->len;
+
+       /* Find phdrs that remap the kernel */
+       kcore_copy__for_each_phdr(kci, p) {
+               u64 pend = p->offset + p->len;
+
+               if (p == k)
+                       continue;
+
+               if (p->offset >= k->offset && pend <= kend)
+                       p->remaps = k;
+       }
+}
+
 static void kcore_copy__layout(struct kcore_copy_info *kci)
 {
        struct phdr_data *p;
        off_t rel = 0;
 
+       kcore_copy__find_remaps(kci);
+
        kcore_copy__for_each_phdr(kci, p) {
-               p->rel = rel;
-               rel += p->len;
+               if (!p->remaps) {
+                       p->rel = rel;
+                       rel += p->len;
+               }
                kci->phnum += 1;
        }
+
+       kcore_copy__for_each_phdr(kci, p) {
+               struct phdr_data *k = p->remaps;
+
+               if (k)
+                       p->rel = p->offset - k->offset + k->rel;
+       }
 }
 
 static int kcore_copy__calc_maps(struct kcore_copy_info *kci, const char *dir,
@@ -1821,6 +1868,8 @@ int kcore_copy(const char *from_dir, const char *to_dir)
        kcore_copy__for_each_phdr(&kci, p) {
                off_t offs = p->rel + offset;
 
+               if (p->remaps)
+                       continue;
                if (copy_bytes(kcore.fd, p->offset, extract.fd, offs, p->len))
                        goto out_extract_close;
        }
-- 
1.9.1