[v3] RISC-V: Always compile mm/init.c with cmodel=medany and notrace

Commit Message

Anup Patel March 25, 2019, 8:31 a.m. UTC

The Linux RISC-V 32bit kernel is broken after we moved setup_vm() from
kernel/setup.c to mm/init.c because Linux RISC-V 32bit kernel by default
uses cmodel=medlow which results in a non-position-independent setup_vm().

This patch fixes Linux RISC-V 32bit kernel booting by:
1. Forcing cmodel=medany for mm/init.c
2. Moving remaing MM-related stuff va_pa_offset, pfn_base and
   empty_zero_page from kernel/setup.c to mm/init.c

Further, the setup_vm() cannot handle GCC epilog/prolog for ftrace so we
disable function tracing for mm/init.c by not using "-pg" compiler flag.

Fixes: 6f1e9e946f0b ("RISC-V: Move setup_vm() to mm/init.c")
Suggested-by: Christoph Hellwig <[e-mail]>
Suggested-by: Mike Rapoport <[e-mail]>
Signed-off-by: Anup Patel <[e-mail]>
Reviewed-by: Mike Rapoport <[e-mail]>
---
v3: Don't use CFLAG "-pg" for mm/init.o
v2: Removed CFLAGS_setup.o from kernel/Makefile and replaced SoBs
---
 arch/riscv/kernel/Makefile |  3 ---
 arch/riscv/kernel/setup.c  |  8 --------
 arch/riscv/mm/Makefile     |  7 +++++++
 arch/riscv/mm/init.c       | 22 ++++++++++++++++++++++
 4 files changed, 29 insertions(+), 11 deletions(-)

--
2.17.1

Comments

Christoph Hellwig March 25, 2019, 11:37 a.m. UTC | #1

> +ifdef CONFIG_FTRACE
> +CFLAGS_REMOVE_init.o = -pg
> +endif
> +
>  obj-y += init.o
>  obj-y += fault.o
>  obj-y += extable.o
>  obj-y += ioremap.o
>  obj-y += cacheflush.o
> +
> +CFLAGS_init.o := -mcmodel=medany

Can you keep the two flags adjustments togther, preferably towards
the top of the file?

> +/*
> + * The setup_vm() is called from head.S with MMU-off.

s/The //g

Otherwis looks fine:

Reviewed-by: Christoph Hellwig <[e-mail]>

Anup Patel March 26, 2019, 3:57 a.m. UTC | #2

On Mon, Mar 25, 2019 at 5:08 PM Christoph Hellwig <[e-mail]> wrote:
>
> > +ifdef CONFIG_FTRACE
> > +CFLAGS_REMOVE_init.o = -pg
> > +endif
> > +
> >  obj-y += init.o
> >  obj-y += fault.o
> >  obj-y += extable.o
> >  obj-y += ioremap.o
> >  obj-y += cacheflush.o
> > +
> > +CFLAGS_init.o := -mcmodel=medany
>
> Can you keep the two flags adjustments togther, preferably towards
> the top of the file?

Sure, I will more the flags together.

>
> > +/*
> > + * The setup_vm() is called from head.S with MMU-off.
>
> s/The //g

Okay, I will update.

>
> Otherwis looks fine:
>
> Reviewed-by: Christoph Hellwig <[e-mail]>

Regards,
Anup

Patch

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index f13f7f276639..598568168d35 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -4,7 +4,6 @@ 

 ifdef CONFIG_FTRACE
 CFLAGS_REMOVE_ftrace.o = -pg
-CFLAGS_REMOVE_setup.o = -pg
 endif

 extra-y += head.o
@@ -29,8 +28,6 @@  obj-y	+= vdso.o
 obj-y	+= cacheinfo.o
 obj-y	+= vdso/

-CFLAGS_setup.o := -mcmodel=medany
-
 obj-$(CONFIG_FPU)		+= fpu.o
 obj-$(CONFIG_SMP)		+= smpboot.o
 obj-$(CONFIG_SMP)		+= smp.o
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index ecb654f6a79e..540a331d1376 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -48,14 +48,6 @@  struct screen_info screen_info = {
 };
 #endif

-unsigned long va_pa_offset;
-EXPORT_SYMBOL(va_pa_offset);
-unsigned long pfn_base;
-EXPORT_SYMBOL(pfn_base);
-
-unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
-EXPORT_SYMBOL(empty_zero_page);
-
 /* The lucky hart to first increment this variable will boot the other cores */
 atomic_t hart_lottery;
 unsigned long boot_cpu_hartid;
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index eb22ab49b3e0..c1d79e3d005d 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -1,5 +1,12 @@ 
+
+ifdef CONFIG_FTRACE
+CFLAGS_REMOVE_init.o = -pg
+endif
+
 obj-y += init.o
 obj-y += fault.o
 obj-y += extable.o
 obj-y += ioremap.o
 obj-y += cacheflush.o
+
+CFLAGS_init.o := -mcmodel=medany
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index b379a75ac6a6..8cf9ff1f9058 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -25,6 +25,10 @@ 
 #include <asm/pgtable.h>
 #include <asm/io.h>

+unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
+							__page_aligned_bss;
+EXPORT_SYMBOL(empty_zero_page);
+
 static void __init zone_sizes_init(void)
 {
 	unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
@@ -143,6 +147,11 @@  void __init setup_bootmem(void)
 	}
 }

+unsigned long va_pa_offset;
+EXPORT_SYMBOL(va_pa_offset);
+unsigned long pfn_base;
+EXPORT_SYMBOL(pfn_base);
+
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
 pgd_t trampoline_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);

@@ -172,6 +181,19 @@  void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
 	}
 }

+/*
+ * The setup_vm() is called from head.S with MMU-off.
+ *
+ * Following requirements should be honoured for setup_vm() to work
+ * correctly:
+ * 1) It should use PC-relative addressing for accessing kernel symbols.
+ *    To achieve this we always use GCC cmodel=medany.
+ * 2) The compiler instrumentation for FTRACE will not work for setup_vm()
+ *    so disable compiler instrumentation when FTRACE is enabled.
+ *
+ * Currently, the above requirements are honoured by using custom CFLAGS
+ * for init.o in mm/Makefile.
+ */
 asmlinkage void __init setup_vm(void)
 {
 	extern char _start;