arm-eabi-gcc 4.7升级后的问题

look_w

某一段arm assembly code,之前用 arm-eabi-gcc 4.6版本编译。执行没问题。
但是换成GCC 4.7后有两个问题。
问题一： 生成的BOOTLOADER无法执行；
问题二： 能执行后，某段指令产生ABORT错误。

问题一：
研究GCC 4.7 compiler 升级文 发现， GCC 4.7缺省编译时， 设置为-munaligned-access

• •On ARM, when compiling for ARMv6 (but not ARMv6-M), ARMv7-A, ARMv7-R, or ARMv7-M,
• the new option -munaligned-access is active by default, which for some sources generates
• code that accesses memory on unaligned addresses. This requires the kernel of those
• systems to enable such accesses (controlled by CP15 register c1, refer to ARM documentation).
• Alternatively, or for compatibility with kernels where unaligned accesses are not supported,
• all code has to be compiled with -mno-unaligned-access. Upstream Linux kernel releases have
• automatically and unconditionally supported unaligned accesses as emitted by GCC due to this
• option being active since version 2.6.28.

后来在makefile中强制指定-mno-unaligned-access, 问题一解决。

• STD_CCFLAGS+=-mno-unaligned-access

问题二：原因： arm mode call 的指令编译正常。下载到Trace32里面， memory view显示正常。
但是执行到特定指令时，该arm instruction被解释成为 两条 thumb 指令， 从而导致 abort 错误。
后来发现是从thumb mode 调用 arm call 时，不能正确找到对应的 function symbol. 需要显式声明.

GCC 4.7 升级文档中，可能对应如下说明

• <pre code_snippet_id="157946" snippet_file_name="blog_20140115_3_8233781"
  class="java" name="code">•Link-time optimization (LTO) improvements: ◦Improved scalability and reduced memory usage. Link time optimization of Firefox now requires 3GB of RAM on a 64-bit system, while over 8GB was needed previously. Linking time has been improved, too. The serial stage of linking Firefox has been sped up by about a factor of 10.
• ◦Reduced size of object files and temporary storage used during linking.
• ◦Streaming performance (both outbound and inbound) has been improved.
• ◦ld -r is now supported with LTO.
• ◦Several bug fixes, especially in symbol table handling and merging.</pre><p></p>
• <pre></pre>
• <p></p>
• <p></p>
• <p>具体举例说明如下。</p>
• <pre code_snippet_id="157946" snippet_file_name="blog_20140328_4_9178606"
  class="cpp" name="code">Here is ASM code (file test.S):
• ===========================
•   .syntax unified
•   .text
•   .code 32
•   .global test
•   .func test
• test:
•    nop
•    bx lr
• .endfunc
• Here is C code (file c.c):
• ============================
• void test (void);
• int test2 (void)
• {
•   test();
• }
• Script for compilation
• ============================
• </pre>
• <p><br>
• 编译过程如下</p>
• <pre code_snippet_id="157946" snippet_file_name="blog_20140328_5_4750741"
  class="cpp" name="code">Script for compilation
• ============================
• arm-none-eabi-gcc -c -mcpu=cortex-r4 -mthumb-interwork -Wa,-gdwarf2 -x assembler-with-cpp test.S
• arm-none-eabi-gcc -c -mcpu=cortex-r4 -mthumb -mthumb-interwork -Wa,-gdwarf2 c.c
• arm-none-eabi-gcc -o test.elf -mcpu=cortex-r4 -mthumb -mthumb-interwork -g -nostartfiles test.o c.o
• arm-none-eabi-objdump.exe -d test.elf > test.dump
• </pre>
• <p><br>
• 生成的汇编代码如下</p>
• <p>生成的汇编代码如下:</p>
• <pre code_snippet_id="157946" snippet_file_name="blog_20140328_6_879284"
  class="cpp" name="code">===========================
• Disassembly of section .text:
• 00008000 <test>:
•     8000: e320f000 nop {0}
•     8004: e12fff1e bx lr
• 00008008 <test2>:
•     8008: b580 push {r7, lr}
•     800a: af00 add r7, sp, #0
•     800c: f7ff fff8 bl 8000 <test> ; !!!!!!!!!!!! <- here must be BLX not BL
•     8010: 4618 mov r0, r3
•     8012: bd80 pop {r7, pc}</pre>
• <p> </p>
• <p>解决问题后的正确代码如下:</p>
• <pre code_snippet_id="157946" snippet_file_name="blog_20140115_3_617203"
  class="cpp" name="code"><p>After changing your small test to:
•   .syntax unified
•   .text
•   .code 32
•   .global test
•   .type test, %function
•   .func test
• test:
•    nop
•    bx lr
• .endfunc</p></pre>
• <link rel="stylesheet" href="http://static.blog.csdn.net/public/res-min/markdown_views.css?v=2.0">