diff options
Diffstat (limited to 'nuttx/Documentation/NuttXNxFlat.html')
| -rw-r--r-- | nuttx/Documentation/NuttXNxFlat.html | 25 |
1 files changed, 22 insertions, 3 deletions
diff --git a/nuttx/Documentation/NuttXNxFlat.html b/nuttx/Documentation/NuttXNxFlat.html index 73be5d7b3..4d70ed9c3 100644 --- a/nuttx/Documentation/NuttXNxFlat.html +++ b/nuttx/Documentation/NuttXNxFlat.html @@ -229,13 +229,16 @@ <li><b>Read-Only Data in RAM</b> <ul> <p> - Read-only data must reside in RAM. + With older GCC compilers (at least up to 4.3.3), read-only data must reside in RAM. In code generated by GCC, all data references are indexed by the PIC<sup>2</sup> base register (that is usually R10 or <i>sl</i> for the ARM processors). The includes read-only data (<code>.rodata</code>). Embedded firmware developers normally like to keep <code>.rodata</code> in FLASH with the code sections. But because all data is referenced with the PIC base register, all of that data must lie in RAM. A NXFLAT change to work around this is under investigation<sup>3</sup>. </p> + <p> + Newer GCC compilers (at least from 4.6.3), read-only data is no long GOT-relative, but is now accessed PC-relative. With PC relative addressing, read-only data <i>must</i> reside in the I-Space. + </p> </ul> </li> <li><b>Globally Scoped Function Function Pointers</b> @@ -464,7 +467,7 @@ cat ../syscall/syscall.csv ../lib/lib.csv | sort >tmp.csv <td><br></td> <td><br></td> <td> - <code>abc-nuttx-elf-ld -r -d -warn-common -T binfmt/libnxflat/gnu-nxflat.ld -no-check-sections -o $@ hello.o hello-thunk.o</code> + <code>abc-nuttx-elf-ld -r -d -warn-common -T binfmt/libnxflat/gnu-nxflat-gotoff.ld -no-check-sections -o $@ hello.o hello-thunk.o</code> </td> </tr> <tr> @@ -507,7 +510,7 @@ cat ../syscall/syscall.csv ../lib/lib.csv | sort >tmp.csv In this case, it will link together the module's object files (only <code>hello.o</code> here) along with the assembled <i>thunk</i> file, <code>hello-thunk.o</code> to create the second relocatable object, <code>hello.r2</code>. - The linker script, <code>gnu-nxflat.ld</code> is required at this point to correctly position the sections. + The linker script, <code>gnu-nxflat-gotoff.ld</code> is required at this point to correctly position the sections. This linker script produces two segments: An <i>I-Space</i> (Instruction Space) segment containing mostly <code>.text</code> and a <i>D-Space</i> (Data Space) segment containing <code>.got</code>, <code>.data</code>, and <code>.bss</code> sections. @@ -518,6 +521,22 @@ cat ../syscall/syscall.csv ../lib/lib.csv | sort >tmp.csv The option <code>-no-check-sections</code> is required to prevent the linker from failing because these segments overlap. </p> +<p><b>NOTE:</b> + There are two linker scripts located at <code>binfmt/libnxflat/gnu-nxflat-gotoff.ld</code>. +</p> +<ol> + <li> + <b><code>binfmt/libnxflat/gnu-nxflat-gotoff.ld</code></b>. + Older versions of GCC (at least up to GCC 4.3.3), use GOT-relative addressing to access RO data. + In that case, read-only data (.rodata) must reside in D-Space and this linker script should be used. + </li> + <li> + <b><code>binfmt/libnxflat/gnu-nxflat-pcrel.ld</code></b>. + Newer versions of GCC (at least as of GCC 4.6.3), use PC-relative addressing to access RO data. + In that case, read-only data (.rodata) must reside in I-Space and this linker script should be used. + </li> +</ol> + <p><b>Target 4</b>. Finally, this target will use the <code>hello.r2</code> relocatable object to create the final, NXFLAT module <code>hello</code> by executing <a href="#ldnxflat"><code>ldnxflat</code></a>. |