[PATCH] powerpc: Change SDT argument constraint

[Sandipan Das]

With the 'o' memory constraint, any memory operand which
has an offsettable address is allowed. However, for some
architectures such as powerpc, this allows operands like
the ones shown below in the readelf output from Fedora 26
to be generated.

  $ readelf -n /lib64/libc.so.6 | grep memory_mallopt_mmap_max -A2 -B2
    stapsdt              0x0000006c	NT_STAPSDT (SystemTap probe descriptors)
      Provider: libc
      Name: memory_mallopt_mmap_max
      Location: 0x00000000000a0274, Base: 0x00000000001ccb90, Semaphore: 0x0000000000000000
      Arguments: -4@9 -4@.LANCHOR0+44@toc@l(8) -4@.LANCHOR0+52@toc@l(7)

The second and third argument shown above are both having
operands which are pointers to static data anchors. Since
these static anchors are not included in the symbol table,
they cannot be resolved from the binary itself. So, such
arguments cannot be read via their corresponding markers.

Using the 'Z' memory constraint instead solves this issue
as it will only allow a memory operand that is an indexed
or indirect from a register.

So, for powerpc, we set STAP_SDT_ARG_CONSTRAINT to 'nZr'
but keep it as 'nor' for all other architectures.

Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
---
 includes/sys/sdt.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/includes/sys/sdt.h b/includes/sys/sdt.h
index f85045851..940f74483 100644
--- a/includes/sys/sdt.h
+++ b/includes/sys/sdt.h
@@ -84,8 +84,12 @@
 # define _SDT_ARGFMT(no)		%n[_SDT_S##no]@_SDT_ARGTMPL(_SDT_A##no)
 
 # ifndef STAP_SDT_ARG_CONSTRAINT
+# if defined __powerpc__
+# define STAP_SDT_ARG_CONSTRAINT        nZr
+# else
 # define STAP_SDT_ARG_CONSTRAINT        nor
 # endif
+# endif
 
 # define _SDT_STRINGIFY(x)              #x
 # define _SDT_ARG_CONSTRAINT_STRING(x)  _SDT_STRINGIFY(x)
-- 
2.13.6