Re: MIPS: Handle manual calls of MIPS16 functions with a call stub

Maciej W. Rozycki
2008-02-08T14:23:37Z

[-- Attachment #1: Type: TEXT/PLAIN, Size: 3418 bytes --]

On Mon, 4 Feb 2008, Daniel Jacobowitz wrote:

> This is not how any other target that I know of handles extra PC bits.
> I think it's going to cause a whole lot of other similar problems. I
> am reluctant to add new hooks to support storing additional bits in
> addresses, when at the same time we have hooks that other targets use
> - called from overlapping places - to remove extra bits from addresses.

Well, it is certainly the smallest change that fits the way the MIPS
target is currently handled throughout the toolchain. Not necessarily the
best.

> Honestly, I'm not just trying to be difficult. But having two targets

Of course -- I would not have doubted. I have been around for long
enough.

> solve the same problem in opposite ways makes the core of GDB a mess.
> "Do line table entries include extra non-address bits" is not a
> question that should have different answers on different targets.
> Similarly for function block addresses.

Your proposal sounds clean enough for me to investigate it further. In
fact I have done so to some extent already.

> I think that using mips_pc_is_mips16 can be made to work, by analogy
> to ARM. I'd look at this myself, but I don't think I'm set up to run

It is much more than that, but I think it can be done with some
adjustments to pointer_to_address(), address_to_pointer() and
integer_to_address() methods. If DWARF-2 records could be treated as
pointers (which they are given how the linker processes them) rather than
addresses then such a setup should work. That should be done above the
level of the DWARF-2 interpreter, as losing the LSB from relative data
often contained in records would result in an accumulative error.

Of course further adjustments might be needed to methods like read_pc(),
write_pc() and unwind_pc() (I am not absolutely sure at this point yet)
and perhaps elsewhere. Just as a proof of concept, with some hacks to the
DWARF-2 parser and elsewhere, including but not limited to functions
mentioned, I got down to just three regressions compared to results with
my proposal. Now the question is whether a similar result may be achieved
using properly architected code. I'll have a look at it soon.

> mips16 tests (yet). Should I be able to do this with just the GDB
> simulator and a board file?

I have attached the "mips-sim-sde32" board description file I use and the
necessary linker script. You should be able to use it, though there may
be pitfalls. When running tests you need -Wa,-O0 to disable branch
swapping as it makes MIPS16 code inconsistent with DWARF-2 information in
a fatal way.

> I don't understand. The stub is not annotated with debug information
> in the example you posted earlier in the thread. It's only "inside
> the block" physically in the assembly file and for the purposes of
> confusing gas (it probably puts the symbol and first instruction in
> different frags, the first of which is zero length, breaking whatever
> gas uses to annotate the symbol value). It's not covered by the range
> [.LFB20, .LEB20] because those labels are in the text section.

It is still covered by the .loc directive and therefore recognised to be
a part of the code corresponding to the first line of the function. It
makes single-stepping through it possible -- including correct frame
discovery as required by `nexti'/`step'/`next' (not `stepi' though).

Maciej

[-- Attachment #2: Type: TEXT/PLAIN, Size: 10844 bytes --]

2005-03-17 Nigel Stephens <nigel@mips.com>

[mti-libgloss-linkonce]
* mips/mdi32.ld: Append appending final '.' to .gnu.linkonce.x
input section names, and add missing .gnu.linkonce.b. section.
* mips/mdi64.ld: Similarly.
* mips/sde32.ld: Similarly.
* mips/sde64.ld: Similarly.

2004-11-26 Nigel Stephens <nigel@mips.com>

* mips/sde32.ld: New linker script for SDE newlib configurations,
which uses elf32-trad*mips.

* mips/sde64.ld: Change object formats from elf32-n*mips to elf32-ntrad*mips.

* mips/mdi32.ld: Change object formats from elf32-*mips to elf32-trad*mips.

* mips/mdi64.ld: Change object formats from elf32-n*mips to elf32-ntrad*mips.

* mips/configure.in (mips*-sde-elf*): Change "idt32" in script_list
to "sde32".

* mips/configure: Rebuilt.

2004-10-04 Nigel Stephens <nigel@mips.com>

* mips/idt32.ld (.sdeosabi): Added this new section to the script,
so that we can tell gdb that whether this program uses "SDE"
exception handling or not.
* mips/sde64.ld: Similarly.

2004-08-24 Nigel Stephens <nigel@mips.com>

* mips/mdi32.ld: MDI/MIPSsim link script for 32-bit ABIs.
* mips/mdi64.ld: MDI/MIPSsim link script for N32 ABI.

Index: binutils/src/libgloss/mips/sde32.ld
===================================================================
--- /dev/null
+++ binutils/src/libgloss/mips/sde32.ld
@@ -0,0 +1,175 @@
+/* The following TEXT start address leaves space for the monitor
+ workspace. This linker script links isa32 programs for use with the
+ simulator. */
+
+ENTRY(_start)
+OUTPUT_ARCH("mips:isa32")
+OUTPUT_FORMAT("elf32-tradlittlemips", "elf32-tradbigmips", "elf32-tradlittlemips")
+GROUP(-lc -lidt -lgcc)
+SEARCH_DIR(.)
+__DYNAMIC = 0;
+STARTUP(crt0.o)
+
+/*
+ * Allocate the stack to be at the top of memory, since the stack
+ * grows down
+ */
+PROVIDE (__stack = 0);
+/* PROVIDE (__global = 0); */
+
+/*
+ * Initalize some symbols to be zero so we can reference them in the
+ * crt0 without core dumping. These functions are all optional, but
+ * we do this so we can have our crt0 always use them if they exist.
+ * This is so BSPs work better when using the crt0 installed with gcc.
+ * We have to initalize them twice, so we multiple object file
+ * formats, as some prepend an underscore.
+ */
+PROVIDE (hardware_exit_hook = 0);
+PROVIDE (hardware_hazard_hook = 0);
+PROVIDE (hardware_init_hook = 0);
+PROVIDE (software_init_hook = 0);
+
+SECTIONS
+{
+ . = 0x80020000;
+ .text : {
+ _ftext = . ;
+ PROVIDE (eprol = .);
+ *(.text)
+ *(.text.*)
+ *(.gnu.linkonce.t.*)
+ *(.mips16.fn.*)
+ *(.mips16.call.*)
+ }
+ .init : {
+ KEEP(*(.init))
+ }
+ .fini : {
+ KEEP(*(.fini))
+ }
+ .rel.sdata : {
+ PROVIDE (__runtime_reloc_start = .);
+ *(.rel.sdata)
+ PROVIDE (__runtime_reloc_stop = .);
+ }
+ PROVIDE (etext = .);
+ _etext = .;
+
+ .eh_frame_hdr : { *(.eh_frame_hdr) }
+ .eh_frame : { KEEP (*(.eh_frame)) }
+ .gcc_except_table : { *(.gcc_except_table) }
+ .jcr : { KEEP (*(.jcr)) }
+
+ .ctors :
+ {
+ /* gcc uses crtbegin.o to find the start of
+ the constructors, so we make sure it is
+ first. Because this is a wildcard, it
+ doesn't matter if the user does not
+ actually link against crtbegin.o; the
+ linker won't look for a file to match a
+ wildcard. The wildcard also means that it
+ doesn't matter which directory crtbegin.o
+ is in. */
+
+ KEEP (*crtbegin.o(.ctors))
+
+ /* We don't want to include the .ctor section from
+ from the crtend.o file until after the sorted ctors.
+ The .ctor section from the crtend file contains the
+ end of ctors marker and it must be last */
+
+ KEEP (*(EXCLUDE_FILE (*crtend.o) .ctors))
+ KEEP (*(SORT(.ctors.*)))
+ KEEP (*(.ctors))
+ }
+
+ .dtors :
+ {
+ KEEP (*crtbegin.o(.dtors))
+ KEEP (*(EXCLUDE_FILE (*crtend.o) .dtors))
+ KEEP (*(SORT(.dtors.*)))
+ KEEP (*(.dtors))
+ }
+
+ . = .;
+ .rodata : {
+ *(.rdata)
+ *(.rodata)
+ *(.rodata.*)
+ *(.gnu.linkonce.r.*)
+ }
+ .sdeosabi : {
+ /* SDE OSABI indication for GDB */
+ *(.sdeosabi)
+ }
+ _fdata = ALIGN(16);
+ .data : {
+ *(.data)
+ *(.data.*)
+ *(.data1)
+ *(.gnu.linkonce.d.*)
+ }
+ . = ALIGN(8);
+ _gp = . + 0x8000;
+ __global = _gp;
+ .lit8 : {
+ *(.lit8)
+ }
+ .lit4 : {
+ *(.lit4)
+ }
+ .sdata : {
+ *(.sdata)
+ *(.sdata.*)
+ *(.gnu.linkonce.s.*)
+ }
+ . = ALIGN(4);
+ PROVIDE (edata = .);
+ _edata = .;
+ _fbss = .;
+ .sbss : {
+ *(.sbss .sbss.* .gnu.linkonce.sb.*)
+ *(.scommon)
+ }
+ .bss : {
+ _bss_start = . ;
+ *(.bss .bss.* .gnu.linkonce.b.*)
+ *(COMMON)
+ }
+
+ PROVIDE (end = .);
+ _end = .;
+
+ /* DWARF debug sections.
+ Symbols in the DWARF debugging sections are relative to
+ the beginning of the section so we begin them at 0. */
+
+ /* DWARF 1 */
+ .debug 0 : { *(.debug) }
+ .line 0 : { *(.line) }
+
+ /* GNU DWARF 1 extensions */
+ .debug_srcinfo 0 : { *(.debug_srcinfo) }
+ .debug_sfnames 0 : { *(.debug_sfnames) }
+
+ /* DWARF 1.1 and DWARF 2 */
+ .debug_aranges 0 : { *(.debug_aranges) }
+ .debug_pubnames 0 : { *(.debug_pubnames) }
+
+ /* DWARF 2 */
+ .debug_info 0 : { *(.debug_info .gnu.linkonce.wi.*) }
+ .debug_abbrev 0 : { *(.debug_abbrev) }
+ .debug_line 0 : { *(.debug_line) }
+ .debug_frame 0 : { *(.debug_frame) }
+ .debug_str 0 : { *(.debug_str) }
+ .debug_loc 0 : { *(.debug_loc) }
+ .debug_macinfo 0 : { *(.debug_macinfo) }
+
+ /* SGI/MIPS DWARF 2 extensions */
+ .debug_weaknames 0 : { *(.debug_weaknames) }
+ .debug_funcnames 0 : { *(.debug_funcnames) }
+ .debug_typenames 0 : { *(.debug_typenames) }
+ .debug_varnames 0 : { *(.debug_varnames) }
+}
Index: binutils/src/libgloss/mips/sde64.ld
===================================================================
--- /dev/null
+++ binutils/src/libgloss/mips/sde64.ld
@@ -0,0 +1,176 @@
+/* The following TEXT start address leaves space for the monitor
+ workspace. This linker script links isa32 programs for use with the
+ simulator. */
+
+ENTRY(_start)
+OUTPUT_ARCH("mips:isa64")
+OUTPUT_FORMAT("elf32-ntradlittlemips", "elf32-ntradbigmips", "elf32-ntradlittlemips")
+GROUP(-lc -lidt -lgcc)
+SEARCH_DIR(.)
+__DYNAMIC = 0;
+STARTUP(crt0.o)
+
+/*
+ * Allocate the stack to be at the top of memory, since the stack
+ * grows down
+ */
+PROVIDE (__stack = 0);
+/* PROVIDE (__global = 0); */
+
+/*
+ * Initalize some symbols to be zero so we can reference them in the
+ * crt0 without core dumping. These functions are all optional, but
+ * we do this so we can have our crt0 always use them if they exist.
+ * This is so BSPs work better when using the crt0 installed with gcc.
+ * We have to initalize them twice, so we multiple object file
+ * formats, as some prepend an underscore.
+ */
+PROVIDE (hardware_exit_hook = 0);
+PROVIDE (hardware_hazard_hook = 0);
+PROVIDE (hardware_init_hook = 0);
+PROVIDE (software_init_hook = 0);
+
+SECTIONS
+{
+ . = 0x80020000;
+ .text : {
+ _ftext = . ;
+ PROVIDE (eprol = .);
+ *(.text)
+ *(.text.*)
+ *(.gnu.linkonce.t.*)
+ *(.mips16.fn.*)
+ *(.mips16.call.*)
+ }
+ .init : {
+ KEEP(*(.init))
+ }
+ .fini : {
+ KEEP(*(.fini))
+ }
+ .rel.sdata : {
+ PROVIDE (__runtime_reloc_start = .);
+ *(.rel.sdata)
+ PROVIDE (__runtime_reloc_stop = .);
+ }
+ PROVIDE (etext = .);
+ _etext = .;
+
+
+ .eh_frame_hdr : { *(.eh_frame_hdr) }
+ .eh_frame : { KEEP (*(.eh_frame)) }
+ .gcc_except_table : { *(.gcc_except_table) }
+ .jcr : { KEEP (*(.jcr)) }
+
+ .ctors :
+ {
+ /* gcc uses crtbegin.o to find the start of
+ the constructors, so we make sure it is
+ first. Because this is a wildcard, it
+ doesn't matter if the user does not
+ actually link against crtbegin.o; the
+ linker won't look for a file to match a
+ wildcard. The wildcard also means that it
+ doesn't matter which directory crtbegin.o
+ is in. */
+
+ KEEP (*crtbegin.o(.ctors))
+
+ /* We don't want to include the .ctor section from
+ from the crtend.o file until after the sorted ctors.
+ The .ctor section from the crtend file contains the
+ end of ctors marker and it must be last */
+
+ KEEP (*(EXCLUDE_FILE (*crtend.o) .ctors))
+ KEEP (*(SORT(.ctors.*)))
+ KEEP (*(.ctors))
+ }
+
+ .dtors :
+ {
+ KEEP (*crtbegin.o(.dtors))
+ KEEP (*(EXCLUDE_FILE (*crtend.o) .dtors))
+ KEEP (*(SORT(.dtors.*)))
+ KEEP (*(.dtors))
+ }
+
+ . = .;
+ .rodata : {
+ *(.rdata)
+ *(.rodata)
+ *(.rodata.*)
+ *(.gnu.linkonce.r.*)
+ }
+ .sdeosabi : {
+ /* SDE OSABI indication for GDB */
+ *(.sdeosabi)
+ }
+ _fdata = ALIGN(16);
+ .data : {
+ *(.data)
+ *(.data.*)
+ *(.data1)
+ *(.gnu.linkonce.d.*)
+ }
+ . = ALIGN(8);
+ _gp = . + 0x8000;
+ __global = _gp;
+ .lit8 : {
+ *(.lit8)
+ }
+ .lit4 : {
+ *(.lit4)
+ }
+ .sdata : {
+ *(.sdata)
+ *(.sdata.*)
+ *(.gnu.linkonce.s.*)
+ }
+ . = ALIGN(4);
+ PROVIDE (edata = .);
+ _edata = .;
+ _fbss = .;
+ .sbss : {
+ *(.sbss .sbss.* .gnu.linkonce.sb.*)
+ *(.scommon)
+ }
+ .bss : {
+ _bss_start = . ;
+ *(.bss .bss.* .gnu.linkonce.b.*)
+ *(COMMON)
+ }
+
+ PROVIDE (end = .);
+ _end = .;
+
+ /* DWARF debug sections.
+ Symbols in the DWARF debugging sections are relative to
+ the beginning of the section so we begin them at 0. */
+
+ /* DWARF 1 */
+ .debug 0 : { *(.debug) }
+ .line 0 : { *(.line) }
+
+ /* GNU DWARF 1 extensions */
+ .debug_srcinfo 0 : { *(.debug_srcinfo) }
+ .debug_sfnames 0 : { *(.debug_sfnames) }
+
+ /* DWARF 1.1 and DWARF 2 */
+ .debug_aranges 0 : { *(.debug_aranges) }
+ .debug_pubnames 0 : { *(.debug_pubnames) }
+
+ /* DWARF 2 */
+ .debug_info 0 : { *(.debug_info .gnu.linkonce.wi.*) }
+ .debug_abbrev 0 : { *(.debug_abbrev) }
+ .debug_line 0 : { *(.debug_line) }
+ .debug_frame 0 : { *(.debug_frame) }
+ .debug_str 0 : { *(.debug_str) }
+ .debug_loc 0 : { *(.debug_loc) }
+ .debug_macinfo 0 : { *(.debug_macinfo) }
+
+ /* SGI/MIPS DWARF 2 extensions */
+ .debug_weaknames 0 : { *(.debug_weaknames) }
+ .debug_funcnames 0 : { *(.debug_funcnames) }
+ .debug_typenames 0 : { *(.debug_typenames) }
+ .debug_varnames 0 : { *(.debug_varnames) }
+}

[-- Attachment #3: Type: TEXT/PLAIN, Size: 3047 bytes --]

Index: dejagnu-quilt/dejagnu/baseboards/mips-sim-sde32.exp
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ dejagnu-quilt/dejagnu/baseboards/mips-sim-sde32.exp 2007-05-24 16:25:43.000000000 +0100
@@ -0,0 +1,60 @@
+# Load the generic configuration for this board. This will define a basic
+# set of routines needed by the tool to communicate with the board.
+load_generic_config "sim";
+
+# basic-sim.exp is a basic description for the standard Cygnus simulator.
+load_base_board_description "basic-sim";
+
+# This tells it which directory to look in for the simulator.
+setup_sim mips;
+
+# No multilib flags are set by default.
+process_multilib_options "";
+
+# The compiler used to build for this board. This has *nothing* to do
+# with what compiler is tested if we're testing gcc.
+set_board_info compiler "[find_gcc]";
+#set_board_info needs_status_wrapper 1
+set_board_info gdb,nofileio 1
+
+set_board_info cflags "[libgloss_include_flags] [newlib_include_flags]";
+set_board_info ldflags "[libgloss_link_flags] [newlib_link_flags]";
+set_board_info ldscript "-Tsde32.ld";
+
+# And, it can't do arguments, and doesn't have real signals.
+set_board_info noargs 1;
+set_board_info gdb,nosignals 1;
+
+# For some big C++ benchmarks...
+set_board_info sim,options "--memory-size=0x1000000"
+
+# Skip huge test. The MIPS simulator reports only
+# 2MB of memory.
+set_board_info gdb,skip_huge_test 1
+
+# Tell gdb to assume no fpu for -msoft-float compilation
+if {[string match "*soft-float*" [board_info $board multilib_flags]]} {
+ add_board_info gdb_load_commands "set mipsfpu none"
+}
+
+# Tell gdb to assume no fpu for -msoft-float compilation
+if {[string match "*mno-data-in-code*" [board_info $board multilib_flags]]} {
+ add_board_info sim,options "--spram=on"
+}
+
+#
+# Kludge g++_link_flags routine to explicitly add -lstdc++ to link flags
+# so that we can make sure the it comes *before* newlib and the libgloss
+# target libraries
+#
+proc msim_g++_link_flags { args } {
+ set flags [ msim_orig_g++_link_flags "$args" ]
+ append flags "-lstdc++ "
+ return "$flags"
+}
+
+if { [info procs msim_orig_g++_link_flags ] == "" } {
+ verbose "installing msim_g++_link_flags" 1;
+ rename g++_link_flags msim_orig_g++_link_flags
+ rename msim_g++_link_flags g++_link_flags
+}
Index: dejagnu-quilt/dejagnu/lib/targetdb.exp
===================================================================
--- dejagnu-quilt.orig/dejagnu/lib/targetdb.exp 2007-05-24 16:25:04.000000000 +0100
+++ dejagnu-quilt/dejagnu/lib/targetdb.exp 2007-05-24 16:25:12.000000000 +0100
@@ -73,6 +73,15 @@
}
}

+#
+# Add VALUE to ENTRY for the current board being defined.
+#
+proc add_board_info { entry value } {
+ global board_info board;
+
+ lappend board_info($board,$entry) $value;
+}
+
# Fill in ENTRY with VALUE for the current target.
#
proc set_currtarget_info { entry value } {