[PATCH] [MSP430] PR78838: Do not add section name prefixes when section name is .lowtext

[Jozef Lawrynowicz]

The MSP430 target supports the automatic placement of functions and
data in different memory regions when passing the
"-mdata-region=either" and "-mcode-region=either" options.
MSP430x devices support the large memory model, "-mlarge", which
enables 20 bit pointers, however the vector table across all MSP430
targets only accepts 16-bit pointers. To prevent the use of 20-bit
pointers in the vector table when the large memory model is used, the
MSP430 backend currently places functions specified with the interrupt
attribute in a section called ".lowtext". This section is placed at
the beginning of .text in the MSP430 linker scripts.

PR target/78838 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78838)
reports that a function with the interrupt attribute is placed in a
non-existent section ".either.lowtext" when "-mlarge",
"-mcode-region=either" and "-ffunction-sections" are passed. The
backend has correctly decided to place the function in .lowtext, but
has applied the .either prefix which is undesirable.

No additional .lower/.upper/.either prefixes should be applied to the
section name once it has been placed in .lowtext, the patch below
implements this.

I've built and tested successfully with no regressions reported:
  Target is msp430-unknown-elf
  Host   is x86_64-unknown-linux-gnu

Testsuite variations:
msp430-sim/-mcpu=msp430x/-mlarge/-mdata-region=either/-mcode-region=either

The section .lowtext will only be utilised if the large memory model
is used, which is why I have only tested with this testsuite
variation.
I haven't run the g++ testsuite because msp430-elf doesn't build with
C++ support at the moment:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79242

I don't have write access to the GCC SVN repository, so if this patch
is satisfactory, I would appreciate if someone could commit it for me.
Thanks.

---

2017-02-XX  Jozef Lawrynowicz  <jozef.l@somniumtech.com>

gcc/
PR target/78838
* config/msp430/msp430.c (gen_prefix): Return NULL when section name is .lowtext
(msp430_section_is_lowtext): New function.

gcc/testsuite
PR target/78838
* gcc.target/msp430/interrupt_fn_placement.c: New test

From: Jozef Lawrynowicz <jozef.l@somniumtech.com>
Date: Wed, 15 Feb 2017 13:03:40 +0000
Subject: [PATCH] [MSP430] PR78838: Do not add section name prefixes
 when the section name is .lowtext

---
 gcc/config/msp430/msp430.c                               | 14 ++++++++++++++
 gcc/testsuite/gcc.target/msp430/interrupt_fn_placement.c |  9 +++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/msp430/interrupt_fn_placement.c

diff --git a/gcc/config/msp430/msp430.c b/gcc/config/msp430/msp430.c
index 6f63116..c9dffb1 100644
--- a/gcc/config/msp430/msp430.c
+++ b/gcc/config/msp430/msp430.c
@@ -1808,6 +1808,15 @@ is_critical_func (tree decl = current_function_decl)
   return has_attr (ATTR_CRIT, decl);
 }

+static bool
+msp430_section_is_lowtext (tree decl = current_function_decl)
+{
+  if (decl == NULL_TREE)
+    return false;
+  const char * dec_name = DECL_SECTION_NAME (decl);
+  return dec_name && strcmp (".lowtext", dec_name) == 0;
+}
+
 #undef  TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS
 #define TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS
msp430_allocate_stack_slots_for_args

@@ -2146,6 +2155,11 @@ gen_prefix (tree decl)
   if (has_attr ("section", decl))
     return NULL;

+  /* If the function has been put in the .lowtext section because it
is an interrupt
+   * handler, and the large memory model is used, then do not add any
prefixes. */
+  if (msp430_section_is_lowtext (decl))
+    return NULL;
+
   /* If the object has __attribute__((lower)) then use the ".lower."
prefix.  */
   if (has_attr (ATTR_LOWER, decl))
     return lower_prefix;
diff --git a/gcc/testsuite/gcc.target/msp430/interrupt_fn_placement.c
b/gcc/testsuite/gcc.target/msp430/interrupt_fn_placement.c
new file mode 100644
index 0000000..d5d2113
--- /dev/null
+++ b/gcc/testsuite/gcc.target/msp430/interrupt_fn_placement.c
@@ -0,0 +1,9 @@
+/* { dg-do link } */
+/* { dg-options "-mlarge -mcode-region=either -ffunction-sections" } */
+
+void __attribute__((interrupt(2))) ir_1(void) {
+}
+
+int main(void) {
+  while(1);
+}
--
1.8.3.1