[gdb/symtab] Add producer_is_gas

Add producer_is_gas, a generic way to get the gas version from the
producer string.

Tested on x86_64-linux.

gdb/dwarf2/read.c

@@ -11250,8 +11250,8 @@ check_producer (struct dwarf2_cu *cu)
     cu->producer_is_codewarrior = true;
   else if (producer_is_clang (cu->producer, &major, &minor))
     cu->producer_is_clang = true;
-  else if (startswith (cu->producer, "GNU AS 2.39.0"))
-    cu->producer_is_gas_2_39 = true;
+  else if (producer_is_gas (cu->producer, &major, &minor))
+    cu->producer_is_gas_2_39 = major == 2 && minor == 39;
   else
     {
       /* For other non-GCC compilers, expect their behavior is DWARF version

gdb/producer.c

@@ -81,6 +81,45 @@ producer_is_gcc (const char *producer, int *major, int *minor)
 
 /* See producer.h.  */
 
+bool
+producer_is_gas (const char *producer, int *major, int *minor)
+{
+  if (producer == nullptr)
+    {
+      /* No producer, don't know.  */
+      return false;
+    }
+
+  /* Detect prefix.  */
+  const char prefix[] = "GNU AS ";
+  if (!startswith (producer, prefix))
+    {
+      /* Producer is not gas.  */
+      return false;
+    }
+
+  /* Skip prefix.  */
+  const char *cs = &producer[strlen (prefix)];
+
+  /* Ensure that major/minor are not nullptrs.  */
+  int maj, min;
+  if (major == nullptr)
+    major = &maj;
+  if (minor == nullptr)
+    minor = &min;
+
+  int scanned = sscanf (cs, "%d.%d", major, minor);
+  if (scanned != 2)
+    {
+      /* Unable to scan major/minor version.  */
+      return false;
+    }
+
+  return true;
+}
+
+  /* See producer.h.  */
+
 bool
 producer_is_icc_ge_19 (const char *producer)
 {
@@ -251,6 +290,23 @@ Version 18.0 Beta";
     SELF_CHECK (!producer_is_gcc (flang_llvm_exp, &major, &minor));
     SELF_CHECK (producer_is_llvm (flang_llvm_exp));
   }
+
+  {
+    static const char gas_exp[] = "GNU AS 2.39.0";
+    int major = 0, minor = 0;
+    SELF_CHECK (!producer_is_gcc (gas_exp, &major, &minor));
+    SELF_CHECK (producer_is_gas (gas_exp, &major, &minor));
+    SELF_CHECK (major == 2 && minor == 39);
+
+    static const char gas_incomplete_exp[] = "GNU AS ";
+    SELF_CHECK (!producer_is_gas (gas_incomplete_exp, &major, &minor));
+    SELF_CHECK (!producer_is_gcc (gas_incomplete_exp, &major, &minor));
+
+    static const char gas_incomplete_exp_2[] = "GNU AS 2";
+    SELF_CHECK (!producer_is_gas (gas_incomplete_exp_2, &major, &minor));
+    SELF_CHECK (!producer_is_gcc (gas_incomplete_exp_2, &major, &minor));
+  }
+
 }
 }
 }

gdb/producer.h

@@ -30,6 +30,11 @@ extern int producer_is_gcc_ge_4 (const char *producer);
    is NULL or it isn't GCC.  */
 extern int producer_is_gcc (const char *producer, int *major, int *minor);
 
+/* Returns nonzero if the given PRODUCER string is GAS and sets the MAJOR
+   and MINOR versions when not NULL.  Returns zero if the given PRODUCER
+   is NULL or it isn't GAS.  */
+bool producer_is_gas (const char *producer, int *major, int *minor);
+
 /* Check for Intel compilers >= 19.0.  */
 extern bool producer_is_icc_ge_19 (const char *producer);