Re: [PATCH 2/2] gdbserver: Add linux_get_hwcap

[Pedro Franco de Carvalho <pedromfc at linux dot ibm dot com>]

Hi,

I've copied the patch below.

Note that there is a difference in the interface between linux_get_auxv
and linux_get_hwcap(2), the latter still return both the status and the
entry value, but I didn't want to change all their users.

Also, contrary to the gdb client version (target_auxv_search
gdb/auxv.c), this one doesn't differentiate between an error and the
entry not being found.

Is that ok?

Thanks!

>From 0af6ec5fdbe9e696e10e22b530c52e3c926c5e9c Mon Sep 17 00:00:00 2001
From: Pedro Franco de Carvalho <pedromfc@linux.ibm.com>
Date: Thu, 4 Apr 2019 14:49:37 -0300
Subject: [PATCH] Use linux_get_auxv to get AT_PHDR in the PPC stub

This patch fixes a build error due to a call to ppc_get_auxv that was
left over after linux_get_hwcap and linux_get_hwcap2 were introduced
in:

974c89e0882ddb03e294eca76a9e3d3bef90eacf gdbserver: Add
linux_get_hwcap

Because the missing call fetched AT_PHDR and not AT_HWCAP,
linux_get_auxv is now visible.

This use also required ppc_get_auxv to return a status variable
indicating that the AT_PHDR entry was not found separately from the
actual value of of the auxv entry.  Therefore, the new linux_get_auxv
function is changed to return a status variable and write the entry
value to a pointer passed as an argument.

Note that linux_get_hwcap and linux_get_hwcap2 still use the return
value as both an indicator of that the entry wasn't found and as the
actual value of the entry.

gdb/gdbserver/ChangeLog:
2019-04-DD  Pedro Franco de Carvalho  <pedromfc@linux.ibm.com>

	* linux-low.c (linux_get_auxv): Remove static.  Return auxv entry
	value in argument pointer, return 1 if the entry is found and 0
	otherwise.  Move comment.
	(linux_get_hwcap, linux_get_hwcap2): Use modified linux_get_auxv.
	* linux-low.h (linux_get_auxv): Declare.
	* linux-ppc-low.c (is_elfv2_inferior): Use linux_get_auxv.
---
 gdb/gdbserver/linux-low.c     | 29 +++++++++++++++++++----------
 gdb/gdbserver/linux-low.h     |  8 ++++++++
 gdb/gdbserver/linux-ppc-low.c |  7 +++++--
 3 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 265043f97e..65919c3262 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -7427,11 +7427,10 @@ linux_get_pc_64bit (struct regcache *regcache)
   return pc;
 }
 
-/* Fetch the entry MATCH from the auxv vector, where entries are length
-   WORDSIZE.  If no entry was found, return zero.  */
+/* See linux-low.h.  */
 
-static CORE_ADDR
-linux_get_auxv (int wordsize, CORE_ADDR match)
+int
+linux_get_auxv (int wordsize, CORE_ADDR match, CORE_ADDR *valp)
 {
   gdb_byte *data = (gdb_byte *) alloca (2 * wordsize);
   int offset = 0;
@@ -7442,15 +7441,21 @@ linux_get_auxv (int wordsize, CORE_ADDR match)
     {
       if (wordsize == 4)
 	{
-	  uint32_t *data_p = (uint32_t *)data;
+	  uint32_t *data_p = (uint32_t *) data;
 	  if (data_p[0] == match)
-	    return data_p[1];
+	    {
+	      *valp = data_p[1];
+	      return 1;
+	    }
 	}
       else
 	{
-	  uint64_t *data_p = (uint64_t *)data;
+	  uint64_t *data_p = (uint64_t *) data;
 	  if (data_p[0] == match)
-	    return data_p[1];
+	    {
+	      *valp = data_p[1];
+	      return 1;
+	    }
 	}
 
       offset += 2 * wordsize;
@@ -7464,7 +7469,9 @@ linux_get_auxv (int wordsize, CORE_ADDR match)
 CORE_ADDR
 linux_get_hwcap (int wordsize)
 {
-  return linux_get_auxv (wordsize, AT_HWCAP);
+  CORE_ADDR hwcap = 0;
+  linux_get_auxv (wordsize, AT_HWCAP, &hwcap);
+  return hwcap;
 }
 
 /* See linux-low.h.  */
@@ -7472,7 +7479,9 @@ linux_get_hwcap (int wordsize)
 CORE_ADDR
 linux_get_hwcap2 (int wordsize)
 {
-  return linux_get_auxv (wordsize, AT_HWCAP2);
+  CORE_ADDR hwcap2 = 0;
+  linux_get_auxv (wordsize, AT_HWCAP2, &hwcap2);
+  return hwcap2;
 }
 
 static struct target_ops linux_target_ops = {
diff --git a/gdb/gdbserver/linux-low.h b/gdb/gdbserver/linux-low.h
index d825184835..d5d074efc5 100644
--- a/gdb/gdbserver/linux-low.h
+++ b/gdb/gdbserver/linux-low.h
@@ -435,6 +435,14 @@ bool thread_db_thread_handle (ptid_t ptid, gdb_byte **handle, int *handle_len);
 
 extern int have_ptrace_getregset;
 
+/* Search for the value with type MATCH in the auxv vector with
+   entries of length WORDSIZE bytes.  If found, store the value in
+   *VALP and return 1.  If not found or if there is an error, return
+   0.  */
+
+int linux_get_auxv (int wordsize, CORE_ADDR match,
+		    CORE_ADDR *valp);
+
 /* Fetch the AT_HWCAP entry from the auxv vector, where entries are length
    WORDSIZE.  If no entry was found, return zero.  */
 
diff --git a/gdb/gdbserver/linux-ppc-low.c b/gdb/gdbserver/linux-ppc-low.c
index 8deb0ce068..f17f05a0a3 100644
--- a/gdb/gdbserver/linux-ppc-low.c
+++ b/gdb/gdbserver/linux-ppc-low.c
@@ -1107,10 +1107,13 @@ is_elfv2_inferior (void)
 #else
   const int def_res = 0;
 #endif
-  unsigned long phdr;
+  CORE_ADDR phdr;
   Elf64_Ehdr ehdr;
 
-  if (!ppc_get_auxv (AT_PHDR, &phdr))
+  const struct target_desc *tdesc = current_process ()->tdesc;
+  int wordsize = register_size (tdesc, 0);
+
+  if (!linux_get_auxv (wordsize, AT_PHDR, &phdr))
     return def_res;
 
   /* Assume ELF header is at the beginning of the page where program headers
-- 
2.13.6