* [PATCH v2 1/2] Implement ASM_DECLARE_FUNCTION_NAME using ASM_OUTPUT_FUNCTION_LABEL
2024-01-02 19:41 [PATCH v2 0/2] asan: Align .LASANPC on function boundary Ilya Leoshkevich
@ 2024-01-02 19:41 ` Ilya Leoshkevich
2024-01-04 19:47 ` Jeff Law
2024-01-12 21:47 ` Jan-Benedict Glaw
2024-01-02 19:41 ` [PATCH v2 2/2] asan: Align .LASANPC on function boundary Ilya Leoshkevich
1 sibling, 2 replies; 7+ messages in thread
From: Ilya Leoshkevich @ 2024-01-02 19:41 UTC (permalink / raw)
To: Jakub Jelinek, Jeff Law, Richard Sandiford
Cc: Andreas Krebbel, gcc-patches, Segher Boessenkool,
Stefan Schulze Frielinghaus, Ilya Leoshkevich
gccint recommends using ASM_OUTPUT_FUNCTION_LABEL in
ASM_DECLARE_FUNCTION_NAME, but many implementations use
ASM_OUTPUT_LABEL instead. It's inconsistent and prevents changes to
ASM_OUTPUT_FUNCTION_LABEL from affecting the respective targets.
---
gcc/config/aarch64/aarch64.cc | 2 +-
gcc/config/alpha/alpha.cc | 5 ++---
gcc/config/arm/aout.h | 2 +-
gcc/config/arm/arm.cc | 2 +-
gcc/config/bfin/bfin.h | 16 ++++++++--------
gcc/config/c6x/c6x.h | 2 +-
gcc/config/gcn/gcn.cc | 5 ++---
gcc/config/h8300/h8300.h | 2 +-
gcc/config/ia64/ia64.cc | 5 ++---
gcc/config/mcore/mcore-elf.h | 2 +-
gcc/config/microblaze/microblaze.cc | 3 +--
gcc/config/mips/mips.cc | 19 ++++++++++---------
gcc/config/pa/pa.cc | 3 ++-
gcc/config/riscv/riscv.cc | 2 +-
gcc/config/rs6000/rs6000.cc | 4 ++--
15 files changed, 36 insertions(+), 38 deletions(-)
diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 298477d88bb..e3c72f60d4e 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -24207,7 +24207,7 @@ aarch64_declare_function_name (FILE *stream, const char* name,
/* Don't forget the type directive for ELF. */
ASM_OUTPUT_TYPE_DIRECTIVE (stream, name, "function");
- ASM_OUTPUT_LABEL (stream, name);
+ ASM_OUTPUT_FUNCTION_LABEL (stream, name, fndecl);
cfun->machine->label_is_assembled = true;
}
diff --git a/gcc/config/alpha/alpha.cc b/gcc/config/alpha/alpha.cc
index 6aa93783226..8118255e737 100644
--- a/gcc/config/alpha/alpha.cc
+++ b/gcc/config/alpha/alpha.cc
@@ -7986,8 +7986,7 @@ int num_source_filenames = 0;
/* Output the textual info surrounding the prologue. */
void
-alpha_start_function (FILE *file, const char *fnname,
- tree decl ATTRIBUTE_UNUSED)
+alpha_start_function (FILE *file, const char *fnname, tree decl)
{
unsigned long imask, fmask;
/* Complete stack size needed. */
@@ -8052,7 +8051,7 @@ alpha_start_function (FILE *file, const char *fnname,
if (TARGET_ABI_OPEN_VMS)
strcat (entry_label, "..en");
- ASM_OUTPUT_LABEL (file, entry_label);
+ ASM_OUTPUT_FUNCTION_LABEL (file, entry_label, decl);
inside_function = TRUE;
if (TARGET_ABI_OPEN_VMS)
diff --git a/gcc/config/arm/aout.h b/gcc/config/arm/aout.h
index 49896bb9620..380147aed7d 100644
--- a/gcc/config/arm/aout.h
+++ b/gcc/config/arm/aout.h
@@ -152,7 +152,7 @@
do \
{ \
ARM_DECLARE_FUNCTION_NAME (STREAM, NAME, DECL); \
- ASM_OUTPUT_LABEL (STREAM, NAME); \
+ ASM_OUTPUT_FUNCTION_LABEL (STREAM, NAME, DECL); \
} \
while (0)
#endif
diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
index 0c0cb14a8a4..7ca607b3de1 100644
--- a/gcc/config/arm/arm.cc
+++ b/gcc/config/arm/arm.cc
@@ -21800,7 +21800,7 @@ arm_asm_declare_function_name (FILE *file, const char *name, tree decl)
ARM_DECLARE_FUNCTION_NAME (file, name, decl);
ASM_OUTPUT_TYPE_DIRECTIVE (file, name, "function");
ASM_DECLARE_RESULT (file, DECL_RESULT (decl));
- ASM_OUTPUT_LABEL (file, name);
+ ASM_OUTPUT_FUNCTION_LABEL (file, name, decl);
if (cmse_name)
ASM_OUTPUT_LABEL (file, cmse_name);
diff --git a/gcc/config/bfin/bfin.h b/gcc/config/bfin/bfin.h
index c25f41f6839..60a8d716819 100644
--- a/gcc/config/bfin/bfin.h
+++ b/gcc/config/bfin/bfin.h
@@ -995,14 +995,14 @@ typedef enum directives {
fputc ('\n',FILE); \
} while (0)
-#define ASM_DECLARE_FUNCTION_NAME(FILE,NAME,DECL) \
- do { \
- fputs (".type ", FILE); \
- assemble_name (FILE, NAME); \
- fputs (", STT_FUNC", FILE); \
- fputc (';',FILE); \
- fputc ('\n',FILE); \
- ASM_OUTPUT_LABEL(FILE, NAME); \
+#define ASM_DECLARE_FUNCTION_NAME(FILE, NAME, DECL) \
+ do { \
+ fputs (".type ", FILE); \
+ assemble_name (FILE, NAME); \
+ fputs (", STT_FUNC", FILE); \
+ fputc (';', FILE); \
+ fputc ('\n', FILE); \
+ ASM_OUTPUT_FUNCTION_LABEL (FILE, NAME, DECL); \
} while (0)
#define ASM_OUTPUT_LABEL(FILE, NAME) \
diff --git a/gcc/config/c6x/c6x.h b/gcc/config/c6x/c6x.h
index 26b2f2f0700..790b9627ebe 100644
--- a/gcc/config/c6x/c6x.h
+++ b/gcc/config/c6x/c6x.h
@@ -459,7 +459,7 @@ struct GTY(()) machine_function
c6x_output_file_unwind (FILE); \
ASM_OUTPUT_TYPE_DIRECTIVE (FILE, NAME, "function"); \
ASM_DECLARE_RESULT (FILE, DECL_RESULT (DECL)); \
- ASM_OUTPUT_LABEL (FILE, NAME); \
+ ASM_OUTPUT_FUNCTION_LABEL (FILE, NAME, DECL); \
} \
while (0)
diff --git a/gcc/config/gcn/gcn.cc b/gcc/config/gcn/gcn.cc
index b67551a2e8e..b2528d49de4 100644
--- a/gcc/config/gcn/gcn.cc
+++ b/gcc/config/gcn/gcn.cc
@@ -6555,7 +6555,7 @@ output_file_start (void)
comments that pass information to mkoffload. */
void
-gcn_hsa_declare_function_name (FILE *file, const char *name, tree)
+gcn_hsa_declare_function_name (FILE *file, const char *name, tree decl)
{
int sgpr, vgpr, avgpr;
bool xnack_enabled = TARGET_XNACK;
@@ -6716,8 +6716,7 @@ gcn_hsa_declare_function_name (FILE *file, const char *name, tree)
fputs ("\t.type\t", file);
assemble_name (file, name);
fputs (",@function\n", file);
- assemble_name (file, name);
- fputs (":\n", file);
+ ASM_OUTPUT_FUNCTION_LABEL (file, name, decl);
/* This comment is read by mkoffload. */
if (flag_openacc)
diff --git a/gcc/config/h8300/h8300.h b/gcc/config/h8300/h8300.h
index 311e4023dfd..b62779a9273 100644
--- a/gcc/config/h8300/h8300.h
+++ b/gcc/config/h8300/h8300.h
@@ -650,7 +650,7 @@ struct cum_arg
#define GLOBAL_ASM_OP "\t.global "
#define ASM_DECLARE_FUNCTION_NAME(FILE, NAME, DECL) \
- ASM_OUTPUT_LABEL (FILE, NAME)
+ ASM_OUTPUT_FUNCTION_LABEL (FILE, NAME, DECL)
/* This is how to store into the string LABEL
the symbol_ref name of an internal numbered label where
diff --git a/gcc/config/ia64/ia64.cc b/gcc/config/ia64/ia64.cc
index ac566efcf19..92d00bf922f 100644
--- a/gcc/config/ia64/ia64.cc
+++ b/gcc/config/ia64/ia64.cc
@@ -3886,8 +3886,7 @@ ia64_expand_prologue (void)
/* Output the textual info surrounding the prologue. */
void
-ia64_start_function (FILE *file, const char *fnname,
- tree decl ATTRIBUTE_UNUSED)
+ia64_start_function (FILE *file, const char *fnname, tree decl)
{
#if TARGET_ABI_OPEN_VMS
vms_start_function (fnname);
@@ -3896,7 +3895,7 @@ ia64_start_function (FILE *file, const char *fnname,
fputs ("\t.proc ", file);
assemble_name (file, fnname);
fputc ('\n', file);
- ASM_OUTPUT_LABEL (file, fnname);
+ ASM_OUTPUT_FUNCTION_LABEL (file, fnname, decl);
}
/* Called after register allocation to add any instructions needed for the
diff --git a/gcc/config/mcore/mcore-elf.h b/gcc/config/mcore/mcore-elf.h
index bf1b093d327..3e0b903727b 100644
--- a/gcc/config/mcore/mcore-elf.h
+++ b/gcc/config/mcore/mcore-elf.h
@@ -51,7 +51,7 @@ along with GCC; see the file COPYING3. If not see
} \
ASM_OUTPUT_TYPE_DIRECTIVE (FILE, NAME, "function"); \
ASM_DECLARE_RESULT (FILE, DECL_RESULT (DECL)); \
- ASM_OUTPUT_LABEL (FILE, NAME); \
+ ASM_OUTPUT_FUNCTION_LABEL (FILE, NAME, DECL); \
} \
while (0)
diff --git a/gcc/config/microblaze/microblaze.cc b/gcc/config/microblaze/microblaze.cc
index 3ea177b835e..79405a32dc1 100644
--- a/gcc/config/microblaze/microblaze.cc
+++ b/gcc/config/microblaze/microblaze.cc
@@ -2792,8 +2792,7 @@ microblaze_function_prologue (FILE * file)
ASM_OUTPUT_TYPE_DIRECTIVE (file, fnname, "function");
}
- assemble_name (file, fnname);
- fputs (":\n", file);
+ ASM_OUTPUT_FUNCTION_LABEL (file, fnname, current_function_decl);
if (interrupt_handler && strcmp (INTERRUPT_HANDLER_NAME, fnname))
fputs ("_interrupt_handler:\n", file);
diff --git a/gcc/config/mips/mips.cc b/gcc/config/mips/mips.cc
index 9180dbbf843..be5302b0b7f 100644
--- a/gcc/config/mips/mips.cc
+++ b/gcc/config/mips/mips.cc
@@ -7269,7 +7269,7 @@ mips_gimplify_va_arg_expr (tree valist, tree type, gimple_seq *pre_p,
/* Declare a unique, locally-binding function called NAME, then start
its definition. */
-static void
+static tree
mips_start_unique_function (const char *name)
{
tree decl;
@@ -7291,13 +7291,15 @@ mips_start_unique_function (const char *name)
fputs ("\t.hidden\t", asm_out_file);
assemble_name (asm_out_file, name);
putc ('\n', asm_out_file);
+
+ return decl;
}
/* Start a definition of function NAME. MIPS16_P indicates whether the
function contains MIPS16 code. */
static void
-mips_start_function_definition (const char *name, bool mips16_p)
+mips_start_function_definition (const char *name, bool mips16_p, tree decl)
{
if (mips16_p)
fprintf (asm_out_file, "\t.set\tmips16\n");
@@ -7321,8 +7323,7 @@ mips_start_function_definition (const char *name, bool mips16_p)
ASM_OUTPUT_TYPE_DIRECTIVE (asm_out_file, name, "function");
/* Start the definition proper. */
- assemble_name (asm_out_file, name);
- fputs (":\n", asm_out_file);
+ ASM_OUTPUT_FUNCTION_LABEL (asm_out_file, name, decl);
}
/* End a function definition started by mips_start_function_definition. */
@@ -7349,8 +7350,8 @@ mips_finish_stub (mips_one_only_stub **stub_ptr)
return;
const char *name = stub->get_name ();
- mips_start_unique_function (name);
- mips_start_function_definition (name, false);
+ tree decl = mips_start_unique_function (name);
+ mips_start_function_definition (name, false, decl);
stub->output_body ();
mips_end_function_definition (name);
delete stub;
@@ -7604,7 +7605,7 @@ mips16_build_function_stub (void)
/* Start the function definition. */
assemble_start_function (stubdecl, stubname);
- mips_start_function_definition (stubname, false);
+ mips_start_function_definition (stubname, false, stubdecl);
/* If generating pic2 code, either set up the global pointer or
switch to pic0. */
@@ -7864,7 +7865,7 @@ mips16_build_call_stub (rtx retval, rtx *fn_ptr, rtx args_size, int fp_code)
/* Start the function definition. */
assemble_start_function (stubdecl, stubname);
- mips_start_function_definition (stubname, false);
+ mips_start_function_definition (stubname, false, stubdecl);
if (fp_ret_p)
{
@@ -12064,7 +12065,7 @@ mips_output_function_prologue (FILE *file)
assemble_start_function. This is needed so that the name used here
exactly matches the name used in ASM_DECLARE_FUNCTION_NAME. */
fnname = XSTR (XEXP (DECL_RTL (current_function_decl), 0), 0);
- mips_start_function_definition (fnname, TARGET_MIPS16);
+ mips_start_function_definition (fnname, TARGET_MIPS16, current_function_decl);
/* Output MIPS-specific frame information. */
if (!flag_inhibit_size_directive)
diff --git a/gcc/config/pa/pa.cc b/gcc/config/pa/pa.cc
index 2ee987796f6..cd9210a3ff9 100644
--- a/gcc/config/pa/pa.cc
+++ b/gcc/config/pa/pa.cc
@@ -3991,7 +3991,8 @@ pa_output_function_label (FILE *file)
/* The function's label and associated .PROC must never be
separated and must be output *after* any profiling declarations
to avoid changing spaces/subspaces within a procedure. */
- ASM_OUTPUT_LABEL (file, XSTR (XEXP (DECL_RTL (current_function_decl), 0), 0));
+ const char *name = XSTR (XEXP (DECL_RTL (current_function_decl), 0), 0);
+ ASM_OUTPUT_FUNCTION_LABEL (file, name, current_function_decl);
fputs ("\t.PROC\n", file);
/* pa_expand_prologue does the dirty work now. We just need
diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 0d1cbc5cb5f..974f6d5f917 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -8486,7 +8486,7 @@ riscv_declare_function_name (FILE *stream, const char *name, tree fndecl)
{
riscv_asm_output_variant_cc (stream, fndecl, name);
ASM_OUTPUT_TYPE_DIRECTIVE (stream, name, "function");
- ASM_OUTPUT_LABEL (stream, name);
+ ASM_OUTPUT_FUNCTION_LABEL (stream, name, fndecl);
if (DECL_FUNCTION_SPECIFIC_TARGET (fndecl))
{
fprintf (stream, "\t.option push\n");
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 6b9a40fcc66..6c9f99c6e87 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -21419,7 +21419,7 @@ rs6000_elf_declare_function_name (FILE *file, const char *name, tree decl)
fputs ("\t.long 0\n", file);
fprintf (file, "\t.previous\n");
}
- ASM_OUTPUT_LABEL (file, name);
+ ASM_OUTPUT_FUNCTION_LABEL (file, name, decl);
}
static void rs6000_elf_file_end (void) ATTRIBUTE_UNUSED;
@@ -21992,7 +21992,7 @@ rs6000_xcoff_declare_function_name (FILE *file, const char *name, tree decl)
assemble_name (file, buffer);
fputs (TARGET_32BIT ? "\n" : ",3\n", file);
- ASM_OUTPUT_LABEL (file, buffer);
+ ASM_OUTPUT_FUNCTION_LABEL (file, buffer, decl);
symtab_node::get (decl)->call_for_symbol_and_aliases (rs6000_declare_alias,
&data, true);
--
2.43.0
^ permalink raw reply [flat|nested] 7+ messages in thread* [PATCH v2 2/2] asan: Align .LASANPC on function boundary
2024-01-02 19:41 [PATCH v2 0/2] asan: Align .LASANPC on function boundary Ilya Leoshkevich
2024-01-02 19:41 ` [PATCH v2 1/2] Implement ASM_DECLARE_FUNCTION_NAME using ASM_OUTPUT_FUNCTION_LABEL Ilya Leoshkevich
@ 2024-01-02 19:41 ` Ilya Leoshkevich
2024-01-09 18:55 ` Jeff Law
1 sibling, 1 reply; 7+ messages in thread
From: Ilya Leoshkevich @ 2024-01-02 19:41 UTC (permalink / raw)
To: Jakub Jelinek, Jeff Law, Richard Sandiford
Cc: Andreas Krebbel, gcc-patches, Segher Boessenkool,
Stefan Schulze Frielinghaus, Ilya Leoshkevich
GCC can emit code between the function label and the .LASANPC label,
making the latter unaligned. Some architectures cannot load unaligned
labels directly and require literal pool entries, which is inefficient.
Move the invocation of asan_function_start to
ASM_OUTPUT_FUNCTION_LABEL, which guarantees that no additional code is
emitted. This allows setting the .LASANPC label alignment to the
respective function alignment.
---
gcc/asan.cc | 6 ++----
gcc/config/i386/i386.cc | 2 +-
gcc/config/s390/s390.cc | 2 +-
gcc/defaults.h | 2 +-
gcc/final.cc | 3 ---
gcc/output.h | 4 ++++
gcc/varasm.cc | 14 ++++++++++++++
7 files changed, 23 insertions(+), 10 deletions(-)
diff --git a/gcc/asan.cc b/gcc/asan.cc
index 8d0ffb497cc..48738244aba 100644
--- a/gcc/asan.cc
+++ b/gcc/asan.cc
@@ -1481,10 +1481,7 @@ asan_clear_shadow (rtx shadow_mem, HOST_WIDE_INT len)
void
asan_function_start (void)
{
- section *fnsec = function_section (current_function_decl);
- switch_to_section (fnsec);
- ASM_OUTPUT_DEBUG_LABEL (asm_out_file, "LASANPC",
- current_function_funcdef_no);
+ ASM_OUTPUT_DEBUG_LABEL (asm_out_file, "LASANPC", current_function_funcdef_no);
}
/* Return number of shadow bytes that are occupied by a local variable
@@ -2006,6 +2003,7 @@ asan_emit_stack_protection (rtx base, rtx pbase, unsigned int alignb,
DECL_INITIAL (decl) = decl;
TREE_ASM_WRITTEN (decl) = 1;
TREE_ASM_WRITTEN (id) = 1;
+ DECL_ALIGN_RAW (decl) = DECL_ALIGN_RAW (current_function_decl);
emit_move_insn (mem, expand_normal (build_fold_addr_expr (decl)));
shadow_base = expand_binop (Pmode, lshr_optab, base,
gen_int_shift_amount (Pmode, ASAN_SHADOW_SHIFT),
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 38d515dac04..09fc2b63ee3 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -1640,7 +1640,7 @@ ix86_asm_output_function_label (FILE *out_file, const char *fname,
SUBTARGET_ASM_UNWIND_INIT (out_file);
#endif
- ASM_OUTPUT_LABEL (out_file, fname);
+ assemble_function_label_raw (out_file, fname);
/* Output magic byte marker, if hot-patch attribute is set. */
if (is_ms_hook)
diff --git a/gcc/config/s390/s390.cc b/gcc/config/s390/s390.cc
index a5c36b43972..c871a10506a 100644
--- a/gcc/config/s390/s390.cc
+++ b/gcc/config/s390/s390.cc
@@ -8323,7 +8323,7 @@ s390_asm_output_function_label (FILE *out_file, const char *fname,
asm_fprintf (out_file, "\t# fn:%s wd%d\n", fname,
s390_warn_dynamicstack_p);
}
- ASM_OUTPUT_LABEL (out_file, fname);
+ assemble_function_label_raw (out_file, fname);
if (hw_after > 0)
asm_fprintf (out_file,
"\t# post-label NOPs for hotpatch (%d halfwords)\n",
diff --git a/gcc/defaults.h b/gcc/defaults.h
index 6f095969410..b76734908cd 100644
--- a/gcc/defaults.h
+++ b/gcc/defaults.h
@@ -150,7 +150,7 @@ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
#ifndef ASM_OUTPUT_FUNCTION_LABEL
#define ASM_OUTPUT_FUNCTION_LABEL(FILE, NAME, DECL) \
- ASM_OUTPUT_LABEL ((FILE), (NAME))
+ assemble_function_label_raw ((FILE), (NAME))
#endif
/* Output the definition of a compiler-generated label named NAME. */
diff --git a/gcc/final.cc b/gcc/final.cc
index e6f1b1e166b..5e21aedf8ed 100644
--- a/gcc/final.cc
+++ b/gcc/final.cc
@@ -1686,9 +1686,6 @@ final_start_function_1 (rtx_insn **firstp, FILE *file, int *seen,
high_block_linenum = high_function_linenum = last_linenum;
- if (flag_sanitize & SANITIZE_ADDRESS)
- asan_function_start ();
-
rtx_insn *first = *firstp;
if (in_initial_view_p (first))
{
diff --git a/gcc/output.h b/gcc/output.h
index 76cfd58c1e6..bfdecc5ea74 100644
--- a/gcc/output.h
+++ b/gcc/output.h
@@ -178,6 +178,10 @@ extern void assemble_asm (tree);
/* Get the function's name from a decl, as described by its RTL. */
extern const char *get_fnname_from_decl (tree);
+/* Output function label, possibly with accompanying metadata. No additional
+ code or data is output after the label. */
+extern void assemble_function_label_raw (FILE *, const char *);
+
/* Output assembler code for the constant pool of a function and associated
with defining the name of the function. DECL describes the function.
NAME is the function's name. For the constant pool, we use the current
diff --git a/gcc/varasm.cc b/gcc/varasm.cc
index 69f8f8ee018..d0d670d009c 100644
--- a/gcc/varasm.cc
+++ b/gcc/varasm.cc
@@ -61,6 +61,7 @@ along with GCC; see the file COPYING3. If not see
#include "alloc-pool.h"
#include "toplev.h"
#include "opts.h"
+#include "asan.h"
/* The (assembler) name of the first globally-visible object output. */
extern GTY(()) const char *first_global_object_name;
@@ -1835,6 +1836,19 @@ get_fnname_from_decl (tree decl)
return XSTR (x, 0);
}
+/* Output function label, possibly with accompanying metadata. No additional
+ code or data is output after the label. */
+
+void
+assemble_function_label_raw (FILE *file, const char *name)
+{
+ ASM_OUTPUT_LABEL (file, name);
+ if ((flag_sanitize & SANITIZE_ADDRESS)
+ /* Notify ASAN only about the first function label. */
+ && (in_cold_section_p == first_function_block_is_cold))
+ asan_function_start ();
+}
+
/* Output assembler code for the constant pool of a function and associated
with defining the name of the function. DECL describes the function.
NAME is the function's name. For the constant pool, we use the current
--
2.43.0
^ permalink raw reply [flat|nested] 7+ messages in thread