Hello Wolfgang,
On Fri, 23 Dec 2011 12:29:12 +0100 Wolfgang Denk wd@denx.de wrote:
The code and comment disagreed: the comment claimed that r6...r31 were copied, and consequently the arrays for "src" and "dst" were declared with 26 entries, but the actual code ("lmw r5,0(r3)" and "stmw r5,0(r4)") copied _27_ words (r5 through r31), which resulted in false "POST cpu Error at multi test" messages.
Great! Thanks for fixing this bug!
Acked-by: Anatolij Gustschin agust@denx.de Tested-by: Anatolij Gustschin agust@denx.de
But I wonder why didn't we see it with U-Boot built using older GCC versions.
Since only 26 words will be compared after the test, the issue only shows up if the destination buffer is placed at lower addresses on the stack than the source buffer. In this case the first word in the source buffer is overwritten. GCC 4.6.1 generated code which changed the order of src[] and dst[] on the stack and the hidden bug showed up.
Here is a partial dump of each buffer and additionally a dump of the following word. The buffer address is in parenthesis:
with GCC 4.2.2:
00: src(03e51c74) 0x00000000, dst(03e51cdc) 0x00000000 01: src(03e51c78) 0x00000001, dst(03e51ce0) 0x00000000 ... 25: src(03e51cd8) 0x00000019, dst(03e51d40) 0x00000000 26: src(03e51cdc) 0x00000000, dst(03e51d44) 0x00000000
Test result:
00: src(03e51c74) 0x00000000, dst(03e51cdc) 0x00000000 01: src(03e51c78) 0x00000001, dst(03e51ce0) 0x00000001 ... 25: src(03e51cd8) 0x00000019, dst(03e51d40) 0x00000019 26: src(03e51cdc) 0x00000000, dst(03e51d44) 0x00000000
with GCC 4.6.1:
00: src(03e57cf4) 0x00000000, dst(03e57c8c) 0x00000000 01: src(03e57cf8) 0x00000001, dst(03e57c90) 0x00000000 ... 25: src(03e57d58) 0x00000019, dst(03e57cf0) 0x00000000 26: src(03e57d5c) 0x03f9c3c0, dst(03e57cf4) 0x00000000
Test result: Error at multi test ! 00: src(03e57cf4) 0x03f9c3c0, dst(03e57c8c) 0x00000000 01: src(03e57cf8) 0x00000001, dst(03e57c90) 0x00000001 ... 25: src(03e57d58) 0x00000019, dst(03e57cf0) 0x00000019 26: src(03e57d5c) 0x03f9c3c0, dst(03e57cf4) 0x03f9c3c0
Thanks, Anatolij