From mboxrd@z Thu Jan 1 00:00:00 1970 From: Albert ARIBAUD Date: Fri, 14 Nov 2014 16:26:43 +0100 Subject: [U-Boot] Query on CONFIG_SYS_THUMB_BUILD In-Reply-To: References: <5464DC59.2040707@gmail.com> Message-ID: <20141114162643.53b09a8f@lilith> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hello Simon, On Fri, 14 Nov 2014 07:01:59 -0700, Simon Glass wrote: > Hi Victor, > > On 13 November 2014 09:29, Victor Ascroft wrote: > > Hello, > > > > I am working with a Cortex A5 Freescale Vybrid Processor. Since a thumb build leads to a saving of almost 1 MB for my u-boot image and consequently to faster serial downloads I have been looking at this. Currently enabling this option leads to a hang. > > > > After some debugging I have narrowed the place of hang to "ldr pc, =board_init_r" in arch/arm/lib/crt0.S. My debugging procedure was to put a branch to a small function which just printed a small message with puts, just before the ldr instruction and then a printing a small message with puts just at the start of board_init_r in common/board_r.c . For a non thumb build, the two messages get printed and I can boot to the u-boot prompt. For a thumb build, only the first message before the ldr instruction gets printed. > > > > In crt0.S > > bl debug_print > > ldr pc, =board_init_r > > > > In board_init_r > > puts("In board_init_r\n"); // Right at start > > > > void debug_print(void) > > { > > // Defined in board file > > puts("Debug print\n"); > > } > > > > My assembly knowledge is limited and after some consultation with a senior colleague, he told me things to check. > > > > An object dump of the crt0.o shows a branch to an even address. For thumb, this is expected to be odd. To just try out, I did a change as below > > ldr r3, =board_init_r > > add r3, #1 > > bx r3 > > > > No change with this. My expectation was the compiler/linker/assembler would take care of the requirements, with the CONFIG_SYS_THUMB_BUILD. Frankly speaking I am not sure if this is the complete issue or only a part of it. I have seen patches with regards to OMAP send in by Aneesh V, which made changes of the form .type fn_name, %function to all the low level assembly functions, but, I couldn't dig up much more or variants thereof. Basically, from what I understand, this takes care of specifying .thumb_func for a thumb function or so to speak. > > > > Any pointers? Victor, In addition to Simon's question below on the toolchain, I would like to know which commit you're trying to build. > I tried this on a peach_pi (Samsung Chromebook 2 13") and it worked OK > for me. The code sequence you refer to came out as below for me. > > 23e01e10 : > 23e01e10: e1500001 cmp r0, r1 > 23e01e14: 35802000 strcc r2, [r0] > 23e01e18: 32800004 addcc r0, r0, #4 > 23e01e1c: 3afffffb bcc 23e01e10 > 23e01e20: fa000dec blx 23e055d8 > 23e01e24: fb000deb blx 23e055da > 23e01e28: e1a00009 mov r0, r9 > 23e01e2c: e5991030 ldr r1, [r9, #48] ; 0x30 > 23e01e30: e59ff008 ldr pc, [pc, #8] ; 23e01e40 > > 23e01e34: 02073800 .word 0x02073800 > 23e01e38: 23e41eb0 .word 0x23e41eb0 > 23e01e3c: 23e77bf0 .word 0x23e77bf0 > 23e01e40: 23e057a9 .word 0x23e057a9 > > The 'ldr pc' line is loading from 23e01e40 which does have an odd address. > > What toolchain are you using? I tried with gcc 4.8.2 - including > linaro's 2013.10 release. > > In arch/arm/cpu/armv7/config.mk there is a fallback to armv5 from > armv7-a, and this may cause it to generate Thumb code instead of Thumb > 2. But you should get errors if that happens. > > It's hard to debug with such limited visibility. But if I put a puts() > at the start of board_init_r(), I see it on the serial console. Simon, I believe you've built crt0.S for ARM, not Thumb. > Regards, > Simon > _______________________________________________ > U-Boot mailing list > U-Boot at lists.denx.de > http://lists.denx.de/mailman/listinfo/u-boot Amicalement, -- Albert.