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

[Patrick Brünn]

>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?

Regards,
Patrick
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