util/build-id: Fix address comparison for binaries with LOAD vaddr > 0

build_id_find_nhdr_for_addr() fails to find the build-id if the first LOAD
segment has a virtual address other than 0x0.

For most shared libraries, the first LOAD segment has vaddr=0x0:

    Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
    LOAD           0x000000 0x00000000 0x00000000 0x2d2e26 0x2d2e26 R E 0x1000
    LOAD           0x2d2e54 0x002d3e54 0x002d3e54 0x2e248 0x2f148 RW  0x1000

However, compiling the Intel Vulkan driver as 32-bit binary on Android produces
the following ELF header with vaddr=0x8000 instead:

    Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
    PHDR           0x000034 0x00008034 0x00008034 0x00100 0x00100 R   0x4
    LOAD           0x000000 0x00008000 0x00008000 0x224a04 0x224a04 R E 0x1000
    LOAD           0x225710 0x0022e710 0x0022e710 0x25988 0x27364 RW  0x1000

build_id_find_nhdr_callback() compares the address of dli_fbase from dladdr()
and dlpi_addr from dl_iterate_phdr(). With vaddr > 0, these point to a
different memory address, e.g.:

    dli_fbase=0xd8395000 (offset 0x8000)
    dlpi_addr=0xd838d000

At least on glibc and bionic (Android) dli_fbase refers to the address where
the shared object is mapped into the process space, whereas dlpi_addr is just
the base address for the vaddrs declared in the ELF header.

To compare them correctly, we need to calculate the start of the mapping
by adding the vaddr of the first LOAD segment to the base address.

Note: musl users will need the following patch.
https://git.musl-libc.org/cgit/musl/commit/?id=b3ae7beabb9f0c219bb8a8b63567a01c6530c1ac

Cc: Chad Versace <[email protected]>
Cc: <[email protected]>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104642
Fixes: 5c98d38 "util: Query build-id by symbol address, not library name"
Reviewed-by: Emil Velikov <[email protected]>
Reviewed-by: Tapani Pälli <[email protected]>

1 files changed, 12 insertions, 1 deletions

diff --git a/src/util/build_id.c b/src/util/build_id.c
index 536c74360ea..fb67d160e38 100644
--- a/src/util/build_id.c
+++ b/src/util/build_id.c
@@ -58,7 +58,18 @@ build_id_find_nhdr_callback(struct dl_phdr_info *info, size_t size, void *data_)
 {
    struct callback_data *data = data_;
 
-   if ((void *)info->dlpi_addr != data->dli_fbase)
+   /* Calculate address where shared object is mapped into the process space.
+    * (Using the base address and the virtual address of the first LOAD segment)
+    */
+   void *map_start = NULL;
+   for (unsigned i = 0; i < info->dlpi_phnum; i++) {
+      if (info->dlpi_phdr[i].p_type == PT_LOAD) {
+         map_start = (void *)(info->dlpi_addr + info->dlpi_phdr[i].p_vaddr);
+         break;
+      }
+   }
+
+   if (map_start != data->dli_fbase)
       return 0;
 
    for (unsigned i = 0; i < info->dlpi_phnum; i++) {