* config/tc-mips.c (macro): Add comments explaining the rationale

for Chris' change.

diff --git a/gas/ChangeLog b/gas/ChangeLog
index dd82150bd830408b062e01cbed30852104e5a44f..9c32d9dc65c4204576d962c4eab8f827f5048068 100644 (file)
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,8 @@
+2003-04-09  Alexandre Oliva  <aoliva@redhat.com>
+
+       * config/tc-mips.c (macro): Add comments explaining the rationale
+       for Chris' change.
+
 2003-04-09  Chris Demetriou  <cgd@broadcom.com>
 
        * config/tc-mips.c (macro): Put back `+ 0x8000' in test for 64-bit

diff --git a/gas/config/tc-mips.c b/gas/config/tc-mips.c
index 7fa025169c943d1b41cf5c858e7bbb7e4b1e716e..3204ce9ae30620e8bcd114b9ce145375fa9f7f10 100644 (file)
--- a/gas/config/tc-mips.c
+++ b/gas/config/tc-mips.c
@@ -5846,7 +5846,23 @@ macro (ip)
             range is shifted down by 32768 here.  This code should
             probably attempt to generate 64-bit constants more
             efficiently in general.
-          */
+
+            As an extension for architectures with 64-bit registers,
+            we don't truncate 64-bit addresses given as literal
+            constants down to 32 bits, to support existing practice
+            in the mips64 Linux (the kernel), that compiles source
+            files with -mabi=64, assembling them as o32 or n32 (with
+            -Wa,-32 or -Wa,-n32).  This is not beautiful, but since
+            the whole kernel is loaded into a memory region that is
+            addressible with sign-extended 32-bit addresses, it is
+            wasteful to compute the upper 32 bits of every
+            non-literal address, that takes more space and time.
+            Some day this should probably be implemented as an
+            assembler option, such that the kernel doesn't have to
+            use such ugly hacks, even though it will still have to
+            end up converting the binary to ELF32 for a number of
+            platforms whose boot loaders don't support ELF64
+            binaries.  */
          if ((offset_expr.X_op != O_constant && HAVE_64BIT_ADDRESSES)
              || (offset_expr.X_op == O_constant
                  && !IS_SEXT_32BIT_NUM (offset_expr.X_add_number + 0x8000)