[Xen-devel] [PATCH 3/4] xen/link: Fold .data.read_mostly into .data

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

.data.read_mostly only needs separating from adjacent data by one cache line
to be effective, and placing it adjacent to .data.page_aligned fulfills this
requirement.

For ARM, .ex_table appears to be a vestigial remnant.  Nothing in the
resulting build ever inspects or acts on the contents of the table.  The arm32
build does however have some assembly routines which fill .ex_table.

Drop all of ARM's .ex_table infrastructure, to reduce the size of the compiled
binary, and avoid giving the illusion of exception handling working.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>

Only compile tested on ARM.
---
 xen/arch/arm/arm32/lib/assembler.h | 19 ++-----------------
 xen/arch/arm/xen.lds.S             | 16 +---------------
 xen/arch/x86/xen.lds.S             |  7 ++-----
 3 files changed, 5 insertions(+), 37 deletions(-)

diff --git a/xen/arch/arm/arm32/lib/assembler.h 
b/xen/arch/arm/arm32/lib/assembler.h
index 6de2638..42eaabb 100644
--- a/xen/arch/arm/arm32/lib/assembler.h
+++ b/xen/arch/arm/arm32/lib/assembler.h
@@ -160,13 +160,6 @@
        restore_irqs_notrace \oldcpsr
        .endm
 
-#define USER(x...)                             \
-9999:  x;                                      \
-       .pushsection __ex_table,"a";            \
-       .align  3;                              \
-       .long   9999b,9001f;                    \
-       .popsection
-
 #ifdef CONFIG_SMP
 #define ALT_SMP(instr...)                                      \
 9998:  instr
@@ -247,7 +240,7 @@
 #ifdef CONFIG_THUMB2_KERNEL
 
        .macro  usraccoff, instr, reg, ptr, inc, off, cond, abort, t=T()
-9999:
+
        .if     \inc == 1
        \instr\cond\()b\()\t\().w \reg, [\ptr, #\off]
        .elseif \inc == 4
@@ -256,10 +249,6 @@
        .error  "Unsupported inc macro argument"
        .endif
 
-       .pushsection __ex_table,"a"
-       .align  3
-       .long   9999b, \abort
-       .popsection
        .endm
 
        .macro  usracc, instr, reg, ptr, inc, cond, rept, abort
@@ -288,7 +277,7 @@
 
        .macro  usracc, instr, reg, ptr, inc, cond, rept, abort, t=T()
        .rept   \rept
-9999:
+
        .if     \inc == 1
        \instr\cond\()b\()\t \reg, [\ptr], #\inc
        .elseif \inc == 4
@@ -297,10 +286,6 @@
        .error  "Unsupported inc macro argument"
        .endif
 
-       .pushsection __ex_table,"a"
-       .align  3
-       .long   9999b, \abort
-       .popsection
        .endr
        .endm
 
diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index 2b44e5d..3dc5117 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -94,27 +94,13 @@ SECTIONS
   _erodata = .;                /* End of read-only data */
 
   .data : {                    /* Data */
+       *(.data.read_mostly)
        . = ALIGN(PAGE_SIZE);
        *(.data.page_aligned)
        *(.data)
        *(.data.*)
   } :text
 
-  . = ALIGN(SMP_CACHE_BYTES);
-  .data.read_mostly : {
-       /* Exception table */
-       __start___ex_table = .;
-       *(.ex_table)
-       __stop___ex_table = .;
-
-       /* Pre-exception table */
-       __start___pre_ex_table = .;
-       *(.ex_table.pre)
-       __stop___pre_ex_table = .;
-
-       *(.data.read_mostly)
-  } :text
-
   . = ALIGN(8);
   .arch.info : {
       _splatform = .;
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 9fa6c99..ef11949 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -264,12 +264,9 @@ SECTIONS
   __2M_init_end = .;
 
   __2M_rwdata_start = .;       /* Start of 2M superpages, mapped RW. */
-  . = ALIGN(SMP_CACHE_BYTES);
-  DECL_SECTION(.data.read_mostly) {
-       *(.data.read_mostly)
-  } :text
-
   DECL_SECTION(.data) {
+       *(.data.read_mostly)
+       . = ALIGN(PAGE_SIZE);
        *(.data.page_aligned)
        *(.data)
        *(.data.*)
-- 
2.1.4


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