libsframe: fix sframe_find_fre for pltN entries

To find SFrame stack trace information from an FDE of type
SFRAME_FDE_TYPE_PCMASK, sframe_find_fre () was doing an operation
like,
  (start_ip_offset & 0xff) >= (pc & 0xff), etc.

This is buggy and needs correction.  The mask 0xff should be 0xf (to
work for a pltN entry of size say, 16 bytes).

At this time, the size of the pltN entry is implicitly assumed to be 16
bytes by libsframe.  In next version of the SFrame format, we can encode
this information explicitly in the SFrame FDE.

For now, we should fix the code to at least behave correctly for the
generated code and the generated SFrame stack trace information for the
pltN entries on x86_64.

libsframe/
	* sframe.c (sframe_find_fre): Correct the bitmask used for
	SFrame FDEs of type SFRAME_FDE_TYPE_PCMASK.

diff --git a/libsframe/sframe.c b/libsframe/sframe.c
index a5f4a7f65196f4787ed9ddfb7b6e1d339ed5819b..7308a45ce88e4a06257093c6de2e9a803ff4275c 100644 (file)
--- a/libsframe/sframe.c
+++ b/libsframe/sframe.c
@@ -1066,7 +1066,7 @@ sframe_find_fre (sframe_decoder_ctx *ctx, int32_t pc,
   /* FIXME - the bitmask should be picked per ABI or encoded in the format
      somehow. For AMD64, the pltN entry stub is 16 bytes. */
   if (fde_type == SFRAME_FDE_TYPE_PCMASK)
-    bitmask = 0xff;
+    bitmask = 0xf;
 
   fres = ctx->sfd_fres + fdep->sfde_func_start_fre_off;
   func_start_addr = fdep->sfde_func_start_address;