[U-Boot] fs/fat: device not booting since conversion to dir iterators

[Simon Glass]

Hi Patrick,

On 13 December 2017 at 03:15, Patrick Brünn <P.Bruenn at beckhoff.com> wrote:
>>From: Patrick Brünn
>>Sent: Donnerstag, 30. November 2017 12:22
>>
>>Since commit 8eafae209c35932d9a6560809c55ee4641534236
>>my mx53cx9020_defconfig stopped booting.
>>...
>>It seems important to read into do_fat_read_at_block. If I
>>allocate a temporary buffer and read into that one, I still
>>can't boot. That seems strange to me as, I couldn't find
>>any uninitialized access to do_fat_read_at_block anywhere.
>>
> I believe I finally tracked it down to the linker.
>
> Without accessing do_fat_read_at_block within fat.c, I find
> .bss. do_fat_read_at_block as "discarded input section" in
> my u-boot.map
>
> With a patch like this:
> diff --git a/fs/fat/fat.c b/fs/fat/fat.c
> index d16883fa10..8e70fdbc8d 100644
> --- a/fs/fat/fat.c
> +++ b/fs/fat/fat.c
> @@ -1157,6 +1157,7 @@ int fat_opendir(const char *filename, struct fs_dir_stream **dirsp)
>                 return -ENOMEM;
>         memset(dir, 0, sizeof(*dir));
>
> +       if (do_fat_read_at_block[0])
> +               printf("value doesn't matter, the access is important\n");
> +
>         ret = fat_itr_root(&dir->itr, &dir->fsdata);
>         if (ret)
>                 goto fail_free_dir;
>
> The section isn't discarded and my board boots again.
>
>
> Another workaround would be:
> diff --git a/arch/arm/config.mk b/arch/arm/config.mk
> index 124b44a337..02f61fcc3c 100644
> --- a/arch/arm/config.mk
> +++ b/arch/arm/config.mk
> @@ -17,7 +17,7 @@ CFLAGS_NON_EFI := -fno-pic -ffixed-r9 -ffunction-sections -fdata-sections
>  CFLAGS_EFI := -fpic -fshort-wchar
>
>  LDFLAGS_FINAL += --gc-sections
> -PLATFORM_RELFLAGS += -ffunction-sections -fdata-sections \
> +PLATFORM_RELFLAGS += -ffunction-sections \
>                      -fno-common -ffixed-r9
>  PLATFORM_RELFLAGS += $(call cc-option, -msoft-float) \
>        $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,))
>
> Or a hack like:
> diff --git a/arch/arm/cpu/u-boot.lds b/arch/arm/cpu/u-boot.lds
> index 37d4c605ac..b916cbc733 100644
> --- a/arch/arm/cpu/u-boot.lds
> +++ b/arch/arm/cpu/u-boot.lds
> @@ -219,6 +219,7 @@ SECTIONS
>         }
>
>         .bss_end __bss_limit (OVERLAY) : {
> +               KEEP(*(.bss.do_fat_read_at_block));
>                 KEEP(*(.__bss_end));
>         }
>
> I also tried to mark do_fat_read_at_block as:
> volatile, __used and/or __attribute__((externally_visible))
>
> This doesn't help.
>
> Moving it into fat_write.c doesn't help either(with/without static)
>
> My toolchain is:
> ~/u-boot$ arm-linux-gnueabihf-gcc -v
> Using built-in specs.
> COLLECT_GCC=arm-linux-gnueabihf-gcc
> COLLECT_LTO_WRAPPER=/usr/lib/gcc-cross/arm-linux-gnueabihf/6/lto-wrapper
> Target: arm-linux-gnueabihf
> Configured with: ../src/configure -v --with-pkgversion='Debian 6.3.0-18' --with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-6 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm --disable-libquadmath --enable-plugin --enable-default-pie --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-6-armhf-cross/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-armhf-cross --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-armhf-cross --with-arch-directory=arm --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libgcj --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-sjlj-exceptions --with-arch=armv7-a --with-fpu=vfpv3-d16 --with-float=hard --with-mode=thumb --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=arm-linux-gnueabihf --program-prefix=arm-linux-gnueabihf- --includedir=/usr/arm-linux-gnueabihf/include
> Thread model: posix
> gcc version 6.3.0 20170516 (Debian 6.3.0-18)
>
> ~/u-boot$ arm-linux-gnueabihf-ld -v
> GNU ld (GNU Binutils for Debian) 2.28
>
>
> Does anyone have an idea what else I can try to prevent my linker from removing
> do_fat_read_at_block?

This doesn't seem to be used unless you have enabled CONFIG_FAT_WRITE. Have you?

I wonder if the problem is somewhere else, and the presence of this
buffer is just moving things apart in the data space, and thus masking
the problem?

Regards,
Simon