Simon,
-----Original Message----- From: sjg@google.com [mailto:sjg@google.com] On Behalf Of Simon Glass Sent: Thursday, January 05, 2012 10:07 AM To: Stephen Warren Cc: Wolfgang Denk; Thierry Reding; u-boot@lists.denx.de; Tom Warren Subject: Re: [U-Boot] [PATCH 1/2] tegra2: Always build with USE_PRIVATE_LIBGCC=yes.
Hi Stephen,
On Thu, Jan 5, 2012 at 8:53 AM, Stephen Warren swarren@nvidia.com wrote:
On 01/05/2012 08:50 AM, Wolfgang Denk wrote:
Dear Thierry Reding,
In message <1321524246-5187-2-git-send-email-thierry.reding@avionic-
design.de> you wrote:
The AVP on Tegra2 doesn't boot properly when U-Boot is linked against the GCC provided libgcc. To work around this, always build and link against a private libgcc for Tegra2-based boards.
I notice this patch only now, when pulling in from u-boot-arm.
I will accept this only temporarily. Why don't you use a working tool chain instead, or fix the one you are using?
I believe the issue isn't that the toolchain is broken, but due to the mix of multiple CPU types on Tegra, all of which run the same U-Boot
binary.
U-Boot starts execution on the AVP CPU, an ARMv4(?) CPU. U-Boot then inits the main CPUs, ARMv7 Cortex A9s, and arranges for them to continue running U-Boot.
The libraries included in the toolchain are built for the ARMv7 CPUs, and hence fail to operate correctly when used by the portion of U-Boot which runs on the ARMv4 CPU, presumably due to ISA differences. IIRC, there are overrides in the U-Boot build process such that some/all of U-Boot is built so it'll run on ARMv4 OK, which is why using libgcc built by U-Boot solves this.
Yes that's right, but actually I have never delved into exactly why. Perhaps it is an integer divide or internal memcpy() call early in the code. We might be able to find the offending C library code, given enough time, and perhaps arrange not to call it. A little fragile though.
IIRC, it was a divide that caused an undefined instruction exception. You can run U-Boot w/o the UE_PRIVATE_LIBGCC, and break in w/JTAG and look at the undefined instr shadow regs (sp/lr/pc) and find the opcode that caused the fault pretty easily, again IIRC. But USE_PRIVATE_LIBGCC was intended for just this problem, and works fine.
Tom
Regards, Simon
-- nvpublic