[PATCH] libdwfl: Handle unaligned Phdr 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 <mark@klomp.org>
---
 libdwfl/ChangeLog                    |  6 ++++++
 libdwfl/dwfl_segment_report_module.c | 12 ++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index 6c7e0c4a..ac0fbe0f 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,9 @@
+2021-12-19  Mark Wielaard  <mark@klomp.org>
+
+	* dwfl_segment_report_module.c (dwfl_segment_report_module): Copy
+	ph_buffer and set xlatefrom.d_buf to phdrsp when ph_buffer is not
+	aligned.
+
 2021-12-19  Mark Wielaard  <mark@klomp.org>
 
 	* dwfl_segment_report_module.c (dwfl_segment_report_module): Copy
diff --git a/libdwfl/dwfl_segment_report_module.c b/libdwfl/dwfl_segment_report_module.c
index 7f756392..de190e90 100644
--- a/libdwfl/dwfl_segment_report_module.c
+++ b/libdwfl/dwfl_segment_report_module.c
@@ -461,6 +461,18 @@ dwfl_segment_report_module (Dwfl *dwfl, int ndx, const char *name,
   xlateto.d_buf = phdrsp;
   xlateto.d_size = phdrsp_bytes;
 
+  /* ph_ 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 phdr_align = (class32
+		       ? __alignof__ (Elf32_Phdr)
+		       : __alignof__ (Elf64_Phdr));
+  if (((uintptr_t) ph_buffer & (phdr_align - 1)) != 0)
+    {
+      memcpy (phdrsp, ph_buffer, phdrsp_bytes);
+      xlatefrom.d_buf = phdrsp;
+    }
+
   /* Track the bounds of the file visible in memory.  */
   GElf_Off file_trimmed_end = 0; /* Proper p_vaddr + p_filesz end.  */
   GElf_Off file_end = 0;	 /* Rounded up to effective page size.  */
-- 
2.30.2