Re: [avr-libc-dev] [Patch] Include a device info note section in gcrt1.S

[Senthil Kumar Selvaraj]

On Tue, Oct 14, 2014 at 04:29:19PM +0530, Senthil Kumar Selvaraj wrote:
> On Sat, Oct 11, 2014 at 10:35:22AM +0200, Joerg Wunsch wrote:
> > I finally had a chance to test all this.
> > 
> > For reference, here's the result for an ATmega1281:
> > 
> > % avr-objdump -h -j .note.gnu.avr.deviceinfo -s 
> > avr/lib/avr5/atmega1281/crtm1281.o
> > 
> > avr/lib/avr5/atmega1281/crtm1281.o:     file format elf32-avr
> > 
> > Sections:
> > Idx Name          Size      VMA       LMA       File off  Algn
> >  11 .note.gnu.avr.deviceinfo 00000034  00000000  00000000  0000181c  2**2
> >                   CONTENTS, READONLY
> > Contents of section .note.gnu.avr.deviceinfo:
> >  0000 04000000 23000000 01000000 41565200  ....#.......AVR.
> >  0010 00000000 00000200 00020000 00200000  ............. ..
> >  0020 00000000 00100000 08000000 01000000  ................
> >  0030 00000000                             ....            
> > 
> > 
> > As Senthil Kumar Selvaraj wrote:
> > 
> > > How does the below patch look? Once you guys find it ok, I'll follow it
> > > up with a documentation patch. Note that the part above the
> > > L__desc_start label (and the .balign directive at the end) are there as
> > > per the ELF spec for a note section.
> > 
> > OK, if that's required, we have to stick with that.
> > 
> > Wouldn't the note name string also possibly need padding
> > for alignment behind it?  (In the case of the "AVR\0",
> > it only incidentally aligns the following .long values
> > to a long boundary.)
> 
> Yes, I figured it's only going to be "AVR\0", so I skipped the align
> directive. I'll add it.
> > 
> > For the documentation, please include a C struct definition
> > as explanation:
> > 
> > #define __NOTE_NAME_LEN 4
> > struct __note_gnu_avr_deviceinfo
> > {
> >     struct
> >     {
> >         uint32_t note_name_len;          /* = __NOTE_NAME_LEN */
> >         uint32_t desc_len;
> >         char note_name[__NOTE_NAME_LEN]; /* = "AVR\0" */
> >     }
> >     elfinfo_hdr;
> >     struct
> >     {
> >         uint32_t flash_start;
> >         uint32_t flash_size;
> >         uint32_t sram_start;
> >         uint32_t sram_size;
> >         uint32_t eeprom_start;
> >         uint32_t eeprom_size;
> >         uint32_t offset_table[2];  /* index 0: ... */
> >         // ???
> >     }
> >     avr_desc;
> > };
> 
> Ok, will do.
> > 
> > > +.L__stroffsettab_end:
> > > +    /* String table for storing arbitrary strings.
> > > +    Offsets are stored in the string offset table above */
> > > +.L__strtab_start:
> > > +    .byte 0
> > > +.L__device_name_start:
> > > +    .asciz DEVICE_NAME
> > > +.L__device_name_end:
> > > +    .byte 0
> > > +.L__strtab_end:
> > 
> > I don't quite understand the purpose of the two ".byte 0" definitions.
> 
> I used the standard ELF string table convention - the first and last
> bytes are null. From http://man7.org/linux/man-pages/man5/elf.5.html,
> 
> "String table sections hold null-terminated character sequences,
> commonly called strings.  The object file uses these strings to
> represent symbol and section names.  One references a string as an
> index into the string table section.  The first byte, which is index
> zero, is defined to hold a null byte ('\0').  Similarly, a string
> table's last byte is defined to hold a null byte, ensuring null
> termination for all strings."
> 
> There's no need to follow that convention though - the descriptor's
> layout/interpretation can be arbitrary. If you think it is redundant,
> I'll drop it.
> 
> I'll send a new patch with all the changes.
> 

Does the below patch look good? I've added documentation about the
section's layout to doc/api/sections.dox.

Regards
Senthil

ChangeLog

2014-11-03  Senthil Kumar Selvaraj <address@hidden>

        * crt1/gcrt1.S: Add a note section embedding device info.
        * doc/api/sections.dox: Document it.

diff --git avr-libc/crt1/gcrt1.S avr-libc/crt1/gcrt1.S
index 2d341a4..777bedb 100644
--- avr-libc/crt1/gcrt1.S
+++ avr-libc/crt1/gcrt1.S
@@ -304,3 +304,71 @@ __do_copy_data:
 #endif /* __AVR_ASM_ONLY__ */
 ;      .endfunc
 
+    .section .note.gnu.avr.deviceinfo, "", @note
+#define NOTE_NAME "AVR"
+#ifdef __AVR_DEVICE_NAME__
+    #define DEVICE_NAME STR(__AVR_DEVICE_NAME__)
+#else
+    #define DEVICE_NAME ""
+#endif
+
+    .long .L__note_name_end - .L__note_name_start
+    .long .L__desc_end - .L__desc_start
+    .long 1 ; Type 1 - this is the only known note type for AVR.
+.L__note_name_start:
+    .asciz NOTE_NAME
+    .balign 4
+.L__note_name_end:
+.L__desc_start:
+#ifdef FLASHSTART
+    .long FLASHSTART
+#else
+    .long 0
+#endif
+#ifdef PROGMEM_SIZE
+    .long PROGMEM_SIZE
+#elif FLASHEND > 0
+    .long FLASHEND + 1
+#else
+    .long FLASHEND
+#endif
+    .long RAMSTART
+#ifdef RAMSIZE
+    .long RAMSIZE
+#elif RAMEND > 0
+    .long RAMEND - RAMSTART + 1
+#else
+    .long RAMEND
+#endif
+#ifdef E2START
+    .long E2START
+#else
+    .long 0
+#endif
+#ifdef EEPROM_SIZE
+    .long EEPROM_SIZE
+#elif E2END > 0
+    .long E2END + 1
+#else
+    .long E2END
+#endif
+    /* String offsets table.
+    Index 0 - Size of offset table in bytes
+    Index 1 - Device name byte offset
+    */
+.L__stroffsettab_start:
+.long .L__stroffsettab_end - .L__stroffsettab_start /* Size of index table in 
bytes */
+.long .L__device_name_start - .L__strtab_start /* Byte offset of device name */
+.L__stroffsettab_end:
+    /* String table for storing arbitrary strings.
+    Offsets are stored in the string offset table above */
+.L__strtab_start:
+    .byte 0
+.L__device_name_start:
+    .asciz DEVICE_NAME
+.L__device_name_end:
+    .byte 0
+.L__strtab_end:
+.L__desc_end:
+    .balign 4
+
diff --git avr-libc/doc/api/sections.dox avr-libc/doc/api/sections.dox
index a93dec4..a71f13b 100644
--- avr-libc/doc/api/sections.dox
+++ avr-libc/doc/api/sections.dox
@@ -207,6 +207,51 @@ Unused. User definable.
 Goes into an infinite loop after program termination and completion of any
 _exit() code (execution of code in the .fini9 -> .fini1 sections).
 
+\section sec_dot_note The .note.gnu.avr.deviceinfo Section
+
+This section contains device specific information picked up from the device
+header file and compiler builtin macros. The layout conforms to the standard 
ELF
+note section layout 
(http://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-18048.html).
+
+The section contents are laid out as below.
+
+\code
+#define __NOTE_NAME_LEN 4
+struct __note_gnu_avr_deviceinfo
+{
+    struct
+    {
+        uint32_t namesz;          /* = __NOTE_NAME_LEN */
+        uint32_t descsz;          /* =  size of avr_desc */
+        uint32_t type;            /* = 1 - no other AVR note types exist */
+        char note_name[__NOTE_NAME_LEN]; /* = "AVR\0" */
+    }
+    note_header;
+    struct
+    {
+        uint32_t flash_start;
+        uint32_t flash_size;
+        uint32_t sram_start;
+        uint32_t sram_size;
+        uint32_t eeprom_start;
+        uint32_t eeprom_size;
+        uint32_t offset_table_size;
+        uint32_t offset_table[1];  /* Offset table containing byte offsets into
+                                      string table that immediately follows it.
+                                      index 0: Device name byte offset
+                                    */
+        char str_table [2 +
+          strlen(__AVR_DEVICE_NAME__)]; /* Standard ELF string table.
+                                           index 0 : NULL
+                                           index 1 : Device name
+                                           index 2 : NULL
+                                        */
+    }
+    avr_desc;
+};
+\endcode
+
+
 \section asm_sections Using Sections in Assembler Code
 
 Example: