| Message ID | 20240327054127.633598-1-kconsul@linux.ibm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v3] slof/fs/packages/disk-label.fs: improve checking for DOS boot partitions | expand |
Hi! On Wed, Mar 27, 2024 at 01:41:27AM -0400, Kautuk Consul wrote: > -\ read sector to array "block" > -: read-sector ( sector-number -- ) > +\ read sector to array "block" and return actual bytes read > +: read-sector-ret ( sector-number -- actual-bytes ) What does "-ret" mean? The name could be clearer. Why factor it like this, anyway? Shouldn't "read" always read exactly the number of bytes it is asked to? So, "read-sector" should always read exactly one sector, never more, never less. If an exception happens you can (should!) throw an exception. Which you can then catch at a pretty high level. Segher
Hi! On 2024-03-27 08:43:25, Segher Boessenkool wrote: > Hi! > > On Wed, Mar 27, 2024 at 01:41:27AM -0400, Kautuk Consul wrote: > > -\ read sector to array "block" > > -: read-sector ( sector-number -- ) > > +\ read sector to array "block" and return actual bytes read > > +: read-sector-ret ( sector-number -- actual-bytes ) > > What does "-ret" mean? The name could be clearer. > > Why factor it like this, anyway? Shouldn't "read" always read exactly > the number of bytes it is asked to? So, "read-sector" should always > read exactly one sector, never more, never less. Okay I just thought to return the bytes actually read from that 1 sector so that I could do some checking in the subroutines calling read-sector. > > If an exception happens you can (should!) throw an exception. Which > you can then catch at a pretty high level. Ah, correct. Thanks for the suggestion! I think I will now try to throw an exception from read-sector if all the code-paths imply that a "catch" is in progress. I will try to make some change like this and send out a v4 whenever I have time. > > > Segher
On Thu, Mar 28, 2024 at 10:09:20AM +0530, Kautuk Consul wrote: > On 2024-03-27 08:43:25, Segher Boessenkool wrote: > > If an exception happens you can (should!) throw an exception. Which > > you can then catch at a pretty high level. > Ah, correct. Thanks for the suggestion! I think I will now try to throw > an exception from read-sector if all the code-paths imply that a "catch" > is in progress. Don't try to detect something is trying to catch things. Just throw! Always *something* will catch things (the outer interpreter, if nothing else), anyway. In SLOF this is very explicit: : quit BEGIN 0 rdepth! \ clear nesting stack [ \ switch to interpretation state terminal \ all input and output not redirected BEGIN depth . [char] > emit space \ output prompt refill WHILE space ['] interpret catch \ that is all the default throw/catch \ there is! no special casing needed dup print-status \ "ok" or "aborted" or abort" string REPEAT AGAIN ; The whole programming model is that you can blindly throw a fatal error whenever one happens. You cannot deal with it anyway, it is fatal! That is 98% or so of the exceptions you'll ever see. Very sometimes it is used for non-local control flow. That has its place, but please don't overuse that :-) Segher
Hi, On 2024-03-28 05:47:25, Segher Boessenkool wrote: > On Thu, Mar 28, 2024 at 10:09:20AM +0530, Kautuk Consul wrote: > > On 2024-03-27 08:43:25, Segher Boessenkool wrote: > > > If an exception happens you can (should!) throw an exception. Which > > > you can then catch at a pretty high level. > > Ah, correct. Thanks for the suggestion! I think I will now try to throw > > an exception from read-sector if all the code-paths imply that a "catch" > > is in progress. > > Don't try to detect something is trying to catch things. Just throw! > Always *something* will catch things (the outer interpreter, if nothing > else), anyway. In SLOF this is very explicit: > > : quit > BEGIN > 0 rdepth! \ clear nesting stack > [ \ switch to interpretation state > terminal \ all input and output not redirected > BEGIN > depth . [char] > emit space \ output prompt > refill WHILE > space > ['] interpret catch \ that is all the default throw/catch > \ there is! no special casing needed > dup print-status \ "ok" or "aborted" or abort" string > REPEAT > AGAIN ; > > The whole programming model is that you can blindly throw a fatal error > whenever one happens. You cannot deal with it anyway, it is fatal! > That is 98% or so of the exceptions you'll ever see. Very sometimes it > is used for non-local control flow. That has its place, but please > don't overuse that :-) Okay, in the v4 I just sent I added a catch statement in the open method of disk-label.fs to make sure that there is a catch for this throw. Can you please check that and tell me if I need to remove that CATCH statement ? My idea was that maybe I needed to add an appropriate CATCH statement for this in open. > > > Segher
diff --git a/slof/fs/packages/disk-label.fs b/slof/fs/packages/disk-label.fs index 661c6b0..fa15982 100644 --- a/slof/fs/packages/disk-label.fs +++ b/slof/fs/packages/disk-label.fs @@ -132,11 +132,16 @@ CONSTANT /gpt-part-entry debug-disk-label? IF dup ." actual=" .d cr THEN ; -\ read sector to array "block" -: read-sector ( sector-number -- ) +\ read sector to array "block" and return actual bytes read +: read-sector-ret ( sector-number -- actual-bytes ) \ block-size is 0x200 on disks, 0x800 on cdrom drives block-size * 0 seek drop \ seek to sector - block block-size read drop \ read sector + block block-size read \ read sector +; + +\ read sector to array "block" +: read-sector ( sector-number -- ) + read-sector-ret drop ; : (.part-entry) ( part-entry ) @@ -204,7 +209,8 @@ CONSTANT /gpt-part-entry part-entry>sector-offset l@-le ( current sector ) dup to part-start to lpart-start ( current ) BEGIN - part-start read-sector \ read EBR + part-start read-sector-ret \ read EBR + block-size < IF UNLOOP drop 0 EXIT THEN 1 partition>start-sector IF \ ." Logical Partition found at " part-start .d cr 1+ @@ -279,6 +285,7 @@ CONSTANT /gpt-part-entry THEN count-dos-logical-partitions TO dos-logical-partitions + dos-logical-partitions 0= IF false EXIT THEN debug-disk-label? IF ." Found " dos-logical-partitions .d ." logical partitions" cr @@ -352,6 +359,7 @@ CONSTANT /gpt-part-entry no-mbr? IF drop FALSE EXIT THEN \ read MBR and check for DOS disk-label magic count-dos-logical-partitions TO dos-logical-partitions + dos-logical-partitions 0= IF drop 0 EXIT THEN debug-disk-label? IF ." Found " dos-logical-partitions .d ." logical partitions" cr
While testing with a qcow2 with a DOS boot partition it was found that when we set the logical_block_size in the guest XML to >512 then the boot would fail in the following interminable loop: <SNIP> Trying to load: from: /pci@800000020000000/scsi@3 ... virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! </SNIP> Change the count-dos-logical-partitions Forth subroutine and the Forth subroutines calling count-dos-logical-partitions to check for this access beyond end of device error. After making the above changes, it fails properly with the correct error message as follows: <SNIP> Trying to load: from: /pci@800000020000000/scsi@3 ... virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! virtioblk_transfer: Access beyond end of device! E3404: Not a bootable device! E3407: Load failed Type 'boot' and press return to continue booting the system. Type 'reset-all' and press return to reboot the system. Ready! 0 > </SNIP> Signed-off-by: Kautuk Consul <kconsul@linux.ibm.com> --- slof/fs/packages/disk-label.fs | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)