[PATCH] libdwfl: Handle unaligned Ehdr in dwfl_segment_report_module

[Mark Wielaard]

The xlate functions only handle correctly aligned buffers. But they do
handle src == dest. So if the source buffer isn't aligned correctly
just copy it first into the destination (which is already correctly
aligned).

Signed-off-by: Mark Wielaard <m...@klomp.org>
---
 libdwfl/ChangeLog                    |  5 +++++
 libdwfl/dwfl_segment_report_module.c | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index 18ffc347..6c7e0c4a 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,8 @@
+2021-12-19  Mark Wielaard  <m...@klomp.org>
+
+       * dwfl_segment_report_module.c (dwfl_segment_report_module): Copy
+       buffer and set xlatefrom.d_buf to ehdr when buffer is not aligned.
+
 2021-12-19  Mark Wielaard  <m...@klomp.org>
 
        * dwfl_segment_report_module.c (dwfl_segment_report_module): Check
diff --git a/libdwfl/dwfl_segment_report_module.c 
b/libdwfl/dwfl_segment_report_module.c
index a6d6be85..7f756392 100644
--- a/libdwfl/dwfl_segment_report_module.c
+++ b/libdwfl/dwfl_segment_report_module.c
@@ -367,6 +367,20 @@ dwfl_segment_report_module (Dwfl *dwfl, int ndx, const 
char *name,
   e_ident = ((const unsigned char *) buffer);
   ei_class = e_ident[EI_CLASS];
   ei_data = e_ident[EI_DATA];
+  /* buffer may be unaligned, in which case xlatetom would not work.
+     xlatetom does work when the in and out d_buf are equal (but not
+     for any other overlap).  */
+  size_t ehdr_align = (ei_class == ELFCLASS32
+                      ? __alignof__ (Elf32_Ehdr)
+                      : __alignof__ (Elf64_Ehdr));
+  if (((uintptr_t) buffer & (ehdr_align - 1)) != 0)
+    {
+      memcpy (&ehdr, buffer,
+             (ei_class == ELFCLASS32
+              ? sizeof (Elf32_Ehdr)
+              : sizeof (Elf64_Ehdr)));
+      xlatefrom.d_buf = &ehdr;
+    }
   switch (ei_class)
     {
     case ELFCLASS32:
-- 
2.30.2